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
Recipe by Joanne Eats Well With Others at