A decadent blueberry galaxy cake made with layers of light lemon cake, filled with blueberry buttercream, and decorated to look like outer space!
Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}

The time between Valentine’s Day and Easter in my house is like birthday mania.

In order, there’s my birthday, my grandmother-in-law’s birthday, my sister’s birthday, my husband’s birthday all in quick succession. Followed by Easter and then Remy’s birthday at the end of April. 

Even with the pandemic, when we didn’t actually see people on their birthdays, Remy still insisted on a cake for every. celebration. The virtual ones included.

Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}

If you’re wondering whether I’m tired of making birthday cakes, the answer is NEVER!!!!

They are one of my absolute favorite things to make. 

From coming up with a concept to fit the birthday celebrant’s personality and unique taste, to actually executing the idea, and of course eating the final product…I love it all!

Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}

That is, until it came around to my birthday this year and I just had no idea what to make. As it turns out, there’s a lot of pressure in choosing your own birthday cake and honestly I just feel like I’ve had a lot of decision fatigue lately.

So I did what most moms would do in this situation – consulted my trusty toddler sidekick.

Unfortunately her first ten suggestions were an exuberant SEAWEED CAKE, flavored after her favorite briny crackers.

To which I gagged, and then swiftly vetoed. All ten times.

Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}

Finally, after explaining an infinite number of times why a cake that tastes like the sea is probably not the most delicious or birthday-appropriate treat, Remy seemed to finally understand (I say “seemed” because she promptly suggested seaweed cake for every other birthday that has followed) and suggested an outer space cake as an alternative.

PERFECT, since I remembered seeing this blueberry galaxy cake when I was flipping through my favorite Icing On The Cake cookbook when I was deciding what to make for Christmas. 

I showed her the picture and it was a done deal. 

Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}

This truly gorgeous cake starts with a lemon layer cake that is light, fluffy, and tastes like sunshine. 

It is made with a combination of all purpose and cake flour, which make the cake incredibly soft. Additionally, rather than use whole eggs, which would make it  dense and heavy, it uses egg whites alone to create an almost airy texture. 

The original recipe also called for the inclusion of poppy seeds in the cake batter, which I omitted due to toddler taste preferences. However, feel free to add them back in if you have a less picky cake audience!

Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}

To fill and frost the cake, you’ll make a whipped vanilla buttercream that is incredibly easy to work with and somehow not as cloyingly sweet as the American buttercreams I’ve made before.

Part of the vanilla buttercream is reserved so that it can be infused with blueberry flavor, while the rest left as is and used to frosting the top and sides of the cake. The portion of the buttercream that is reserved for the filling is flavored with a blueberry reduction that adds both deep blue hue and fruity flavor to the frosting.

(A word to the wise – when filling the cake, remember to reserve a few tablespoons of the blueberry buttercream to decorate the outside of the cake later!) 

Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}

The technique for getting the galactic, almost ephemeral look to the outside of the cake is called the watercolor effect, so-named because of how the colors almost bleed into each other and create this sort of whirlwind of beautiful color.

To do this, you first need to fill and frost your cake with a solid white layer of buttercream. This will be the backdrop against which the rest of the color is added. 

Next, color a few tablespoons of your white buttercream with whatever colors you want to use to get the desired effect. For a galaxy effect, you’ll want to use blue and lavender. Using a small offset spatula, dab the different colors of buttercream randomly around the tops and sides of the cake so that you get little touches of it interspersed with the white. Next you’ll use a large bench scraper or icing smoother to scrape the sides and bottom of the cake, which will pull the various colors into each other. Tessa (the author of the cookbook this cake comes from) has a great tutorial on her site with video so you can see the process, which I highly recommend!

Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}

For finishing touches, the cake is topped with black- and blueberries that have been dusted with gold or silver luster powder to make them sparkle and shine, as well as sprinkles. Because, well. SPRINKLES!!

I should say that I was very hesitant to tackle this cake because I was sure it would look nothing like the photo in the book, but Tessa’s instructions and recipes are so foolproof that I shouldn’t have worried. If you’re into decadent and gorgeous cakes and desserts, then you need to check out her cookbooks. They are gems and have been heavily used in the past few months for birthday celebrations!

Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}

Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}
A decadent blueberry galaxy cake made with layers of light lemon cake, filled with blueberry buttercream, and decorated to look like outer space!
Yield: 12 servings
For the lemon cake
  • 1.5 cups (195 g) cake flour
  • 1.5 cups + 2 tbsp (205 g) all purpose flour
  • 2 tsp baking powder
  • ½ tsp baking soda
  • ½ tsp kosher salt
  • 2 cups (400 g) sugar
  • finely grated zest of 1 large lemon
  • ½ cup (120 ml) sour cream
  • ¾ cup (180 ml) whole milk
  • 1 cup (225 g) unsalted butter, room temperature
  • 1 tsp vanilla extract
  • 6 large egg whites, gently whisked
  • ¼ cup (60 ml) fresh lemon juice
For the vanilla and blueberry buttercreams
  • 2 cups (450 g) unsalted butter, room temperature
  • 7-8 cups (1 kg) powdered sugar
  • 4 tbsp (60 ml) whole milk
  • 1 tbsp vanilla extract
  • 1 cup (!45 g) fresh blueberries
  • juice of 1 medium lemon
To assemble and decorate
  • gel food coloring
  • ½ cup (75 g) mixed fresh blueberries and blackberries
  • gold or silver luster dust
  • sprinkles
For the lemon cake
  1. Heat oven to 350F (175C). Grease three 8-inch cake pans, then line with parchment paper. Set aside.
  2. In a large bowl, whisk together the flours, baking powder, baking soda, and salt. Set aside.
  3. In a small bowl, combine the sugar and lemon zest. Using your fingers, rub the lemon zest into the sugar until fragrant and starting to look a bit like wet sand. Set aside.
  4. In a measuring bowl or cup, combine the sour cream and milk. Set aside.
  5. In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar-zest mixture on medium-high speed until light and fluffy, about 5 minutes. Scrape down the sides of the bowl, then add in the vanilla. Mix to combine. Add the egg whites, a bit at a time, mixing until incorporated after each addition. Add the lemon juice and mix until combined. Scrape down the sides of the bowl.
  6. Turn the mixer speed to low, then add the flour mixture in two batches, alternating with the milk mixture. After the last addition, mix until just combined and there are no more flour streaks left.
  7. Divide the batter evenly among the prepared baking pans. Place in the oven and bake for 23-28 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool in their pans on a wire rack for 10-15 minutes, then flip out of the pans and cool completely right-side-up on a wire rack. Level the tops of the cooled cakes as needed.
For the buttercream
  1. Combine the butter, 7 cups of the powdered sugar, the milk, and the vanilla in the bowl of a stand mixer fitted with the paddle attachment. Mix on low speed until all of the powdered sugar is incorporated, then increase the mixer speed to medium-high and mix for 3-5 minutes or until light and fluffy. Add the remaining 1 cup of powdered sugar as needed to reach the desired consistency (soft and spreadable).
  2. Set aside 2 cups of the buttercream in a medium bowl; this will be for the blueberry buttercream.
  3. In a small saucepan, combine the blueberries and lemon juice. Simmer over medium heat for 5-10 minutes, or until the blueberries are broken down. Strain through a fine-mesh sieve over a bowl, pressing down on the blueberries to get out as much juice as possible. Discard the solids. Beat together the 2 cups of buttercream with 2 tbsp of the blueberry juice. Add another tbsp of blueberry juice to enhance the color, as desired.
To assemble
  1. Place one cake layer on a serving plate or cake board. Fill a piping bag with a large round tip with the vanilla buttercream. Pipe a ring around the edges of the cake to make a dam. Set aside 3 tbsp of the blueberry buttercream to use for later, then fill the center of the cake with half of the remaining blueberry buttercream, smoothing it into an even layer. Top with a second cake layer and repeat. Place the final cake layer on top.
  2. Frost the cake lightly with the vanilla buttercream to make a crumb coat. Chill in the refrigerator or freezer for 15 minutes to set the frosting.
  3. Set aside ½ cup of the vanilla buttercream, then frost the cake with the remaining vanilla buttercream. Divide the reserved vanilla buttercream into two smalls bowls. Use the gel food coloring to tint one bowl blue and the other lavender.
  4. Use a small offset spatula to randomly dab the various colored vanilla frosting and the blueberry frosting around the tops and sides of the cake.
  5. Hold an icing smoother against the sides of the cake and, using a spinning cake stand), spin the cake so that it rotates around one time. Clean off the icing smoother and repeat until the desired watercolor effect is created. Repeat with the top of the cake.
  6. Arrange the berries on the top of the cake as desired. Brush with the gold or silver luster dust. Decorate with sprinkle as desired.
Recipe adapted slightly from Icing on the Cake


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One Response to Blueberry Galaxy Cake {Lemon Layer Cake with Blueberry Buttercream}

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