Lattice-Topped Raspberry Rhubarb Slab Pie
 
 
A lattice-topped raspberry rhubarb slab pie that is perfect for a summer party! It makes enough to serve a crowd and is perfect with a dollop of vanilla ice cream on top.
Yield: 12-15 servings
Ingredients
For the crust
  • 48 tbsp (678 g) unsalted butter, cold, divided
  • 5 cups (600 g) all purpose flour, divided
  • 1¼ cups (300 g) whole wheat pastry flour, divided
  • 6 tbsp (76 g) sugar, divided
  • 3 tsp (18 g) fine sea salt, divided
  • 1 cup (236 g) water, cold, divided
For the filling
  • 1½ lb (681 g) rhubarb
  • 1 lb (454 g) raspberries
  • 2 cups (400 g) sugar
  • zest of 1 orange
  • 2 vanilla beans
  • ¼ cup + 2 tbsp (44 g) arrowroot powder
  • 1 tsp fine sea salt
For baking the pie
  • 1 large egg
  • pinch of fine sea salt
  • 2 tbsp (26 g) demerara sugar
Instructions
For the crust
  1. Cut half of the butter (24 tbsp, 339 g) into ½-inch thick pieces. Lay the pieces on a plate in a single layer and place in the freezer for 10 minutes.
  2. Combine half of the all purpose flour (300 g), half of the whole wheat pastry flour (150 g), half of the sugar (38 g), and half of the salt (9 g) in the bowl of a stand mixer fitted with the paddle attachment. Mix for 1 minute on low speed to combine.
  3. Remove the butter from the freezer and add it to the mixer bowl. Mix on low speed for 1-2 minutes, or until it is mostly coarse crumbs with some larger pieces of butter mixed in.
  4. Add half of the cold water (118 g) to the bowl and mix on low speed until it just starts to come together.
  5. Pour onto a clean work surface and pat into a rectangular block. Place onto a long sheet of plastic wrap and top with another sheet of plastic wrap. Run a rolling pin over the dough until it is ½-inch thick. Wrap completely in plastic wrap and place in the refrigerator to chill for at least 2 hours or overnight.
  6. Repeat with the remaining half of the ingredients.
  7. When ready to bake, remove both blocks of dough from the refrigerator and allow them to rest on the counter for 10-15 minutes.
  8. Grease the bottom and sides of a jelly roll pan with butter and set aside.
  9. Unwrap one block of dough and place on a lightly floured work surface. Roll into a 15x20 inch rectangle. Place on the prepared jelly roll pan and guide the dough into the creases and sides of the pan. Trim the dough so that there is a 1-inch overhang. Gather the trimmings and pan them into a thin square block. Place the pan with the crust in it and the block of trimmings into the fridge.
  10. For the lattice, dust the work surface again with for and roll the second block of dough into a 15x20-inch rectangle.
  11. Turn a baking sheet upside down and top with parchment paper. Place the rolled out dough onto the baking sheet, folding over the edges if necessary. Place in the refrigerator and chill for 30 minutes.
  12. Remove the block of dough trimmings from the fridge and roll into a 12-inch square. Slide onto a piece of parchment paper and place on top of the rolled out dough. Chill for 30 minutes. Remove from the fridge and cut into 1-inch strips. Remove the lattice dough from the fridge and place on a work surface with the short edge facing you. Cut lengthwise into 1-inch strips. Place all of the strips back in the refrigerator while you prepare the filling.
For the filling
  1. Trim the rhubarb and cut into ½-inch thick pieces. Place in a large bowl with the raspberries. Set aside.
  2. In a medium bowl, combine the sugar with the orange zest and the seeds of 2 vanilla beans. Use your fingers mix the orange zest and vanilla beans into the sugar. Add the arrowroot powder and salt to the sugar. Mix to combine. Add to the bowl with the rhubarb and raspberries. Gently mix until well combined.
  3. Remove the pie shell from the refrigerator and scoop the filling into it, using a spatula to spread it into an even layer.
  4. Remove the lattice strips from the refrigerator. Spread 7 of the long strips evenly across the pie. Weave in the shorter strips to form a woven lattice top. Trim the edges so that the lattice is flush with the inside rim of the pan.
  5. Gently roll the overhang of the dough up to the rim of the pan. Crimp to seal. Place in the refrigerator to chill for 30 minutes.
For baking the pie
  1. Heat oven to 375F.
  2. Remove the pie from the refrigerator.
  3. In a small bowl, whisk the egg with the salt to make an egg wash. Brush over the pie dough and sprinkle the sugar on top.
  4. Place on a parchment-lined baking sheet and bake for 50-60 minutes or until the filling is bubble and the crust is golden, rotating halfway through.
  5. Remove to a cooling rack and allow to cool for at least 1 hour before serving.
Notes
Recipe from A Good Bake
Recipe by Joanne Eats Well With Others at https://joanne-eatswellwithothers.com/2022/08/lattice-topped-raspberry-rhubarb-slab-pie.html