Make the crust: In a large bowl, beat butter and sugar together until completely creamy. Beat in egg and vanilla until smooth. Combine flour, baking powder, and salt. Beat flour mixture into liquid until a soft dough forms.
Press into the bottom and halfway up the sides of a parchment paper-lined 9x13 baking dish. Prick dough all over with a fork. Bake crust at 350F 20 minutes or until just slightly golden. Remove from oven and set aside.
In a large bowl, whisk pumpkin puree, sugar, eggs pumpkin pies spice, salt, cornstarch, vanilla, milk, and bourbon until smooth. Pour pumpkin filling into pre-baked crust.
Bake pan pie at 350F 25-30 minutes or until filling is firm and a knife inserted in middle comes out clean. Cool pumpkin pan pie completely before cutting into squares and serving with whipped cream. Enjoy!