Preheat oven to 400 degrees F. Lightly grease an 8-inch square baking dish. Let pie crusts sit at room temperature 10 to 15 minutes to soften.
In a large skillet, melt 1 tablespoon butter over medium heat. Add thawed and drained peaches and cook 4 to 5 minutes to release excess moisture. Stir in brown sugar, lemon juice, vanilla, and bourbon if using. Simmer 3 to 5 minutes until slightly syrupy. Remove from heat and stir in cornstarch, cinnamon, nutmeg, allspice, and salt. Let cool 5 to 10 minutes.
Unroll one pie crust and press into the bottom and up the sides of the prepared baking dish. Trim excess.
Pour cooled peach filling into the crust. Dot with butter pieces.
Unroll second crust and cut into 1-inch-wide strips. Weave into a lattice pattern over the filling. Trim and press edges to seal.
Whisk egg yolk and milk together. Brush over the crust and sprinkle with sugar.
Place dish on a baking sheet. Bake 40 to 45 minutes until crust is golden brown and filling is bubbling.
Cool 15 to 20 minutes before serving. Serve warm with vanilla ice cream or whipped cream.