Prepare the Baking Tray
Preheat the oven to 350°F (180°C).
Line a large baking tray with parchment paper to prevent sticking.
Roll Out the First Dough Square
Lightly flour a clean surface and roll out the first square of dough into a rectangle slightly larger than 12x8 inches and 1/4-inch thick.
Trim the edges with a sharp knife for a neat finish.
Use a rolling pin to transfer the dough to the prepared baking tray.
Brush Edges with Egg Wash
Beat the egg in a small bowl and brush the edges of the dough with the egg wash.
Spread the Strawberry Jam
Evenly spread the strawberry jam over the dough, avoiding the egg-washed edges to prevent leaking during baking.
Roll Out and Add the Top Crust
Roll out the second square of dough to the same size and thickness as the first.
Carefully place it over the jam-covered base, aligning the edges.
Seal and Crimp the Edges
Press the edges of the dough together with your fingers.
Use a fork to crimp the edges all around to seal the filling inside.
Poke Holes and Bake
Use the fork to poke 3–4 small holes in the top crust to allow steam to escape.
Brush the top with egg wash and bake for 20–25 minutes, or until golden brown.
Cool the Pie
Remove the slab pie from the oven and let it cool on the tray for 45 minutes before decorating.
Prepare the Glaze and Decorate
In a medium bowl, whisk powdered sugar, milk, and vanilla extract until smooth.
Pour the glaze over the cooled pie and spread evenly with the back of a spoon.
Sprinkle rainbow sprinkles on top and let the glaze set for 5–10 minutes.
Slice and Serve
Use a sharp knife to cut the slab pie into 8 equal pieces.
Serve with a glass of milk or as a delightful dessert on its own.
