Not unlike an oversized breakfast pastry, this Cookie Butter Brown Sugar Slab Pie is loaded with tons of cinnamon, butterscotch flavor in a flaky, buttery crust. The pie is baked thin in a sheet pan then cut into squares for sharing. A bit of cinnamon in the filling and glaze pairs perfectly with the cookie butter filling, also known as speculoos or Biscoff. Serve it up warm with a scoop of ice cream or eat out of hand for an on-the-go treat!
If you don’t have a quarter sheet pan, you can make a free-form slab pie. Roll the dough to the same dimensions and place on a parchment lined baking sheet. Add the filling to the bottom but leave a 1-inch border around the edges. Seal the two layers of pie dough by crimping or press down with the tines of a fork around the edges before baking.
Related: No-Bake Biscoff Cheesecake
Preheat oven to 375°F. Roll out half the amount of pie dough into a rectangle, about 12 x 16-inches. Line the bottom of a 9 x 13-inch quarter sheet pan with parchment paper. Fit the dough into the pan. Allow an inch or so of dough to overhang the edges.
Scoop ½ cup of the cookie butter onto the dough. Spread with a spatula to cover the dough.
In a small bowl, stir together the brown sugar, flour, 1 ½ teaspoons cinnamon and salt.
Sprinkle the sugar mixture all over the cookie butter.
Roll out the second half of the dough into a rectangle, about 11 x 15-inches. Whisk the egg with a splash of water to create an egg wash. Brush the edges of the bottom piece of dough with egg wash.
Place the second piece of dough on top of the pie, pressing the edges together to seal. Trim the edges as needed. Crimp the edges together. Pierce the top of the pie with a paring knife a few times then brush all over with the egg wash.
Set the pie on top of a large rimmed baking sheet and into the oven. Bake for about 35 minutes, or until puffed and golden brown. Allow to cool before adding the glaze.
To make the glaze, stir together the powdered sugar, ½ tsp cinnamon, 1 tablespoon milk, and vanilla extract. The glaze should be smooth and pourable, but not runny. Add more milk as needed.
Spoon the glaze onto the cooled pie. Fill a piping bag (or a zip-top plastic bag with the corner snipped off) with a scoop of cookie butter. Squeeze the cookie butter over the top of the glaze.
Slice and enjoy!