Preheat the oven to 350F then line a baking sheet with parchement paper and set aside.
Cream the butter, peanut butter, brown sugar, and granulated sugar. Add in the eggs and vanilla extract then mix until combined.
1/2 cup smooth peanut butter, 1/2 cup butter, 1/2 cup brown sugar, 1/3 cup granulated sugar, 1 egg at room temperature, 1/2 tsp vanilla extract
Add in the flour baking powder, baking soda, corn starch, and salt, and mix just until the flour mixture disappears.
1 & 1/3 cup all-purpose flour, 1/2 tsp baking powder, 1/2 tsp baking soda, 1 tbsp corn starch, 1/4 tsp salt
Using a large cookie scooper, scoop out 9 equally sized cookie dough balls, place them on a baking sheet, and gently flatten to about 3/4 inch in thickness. Bake in the preheated oven for 9 minutes.