Mix flours, powder, soda, cornstarch, and salt in a large bowl.
1 cup all-purpose flour, 1⅓ cup cake flour, 1 teaspoon baking soda, 1 teaspoon baking powder, 1 tablespoon cornstarch, 1 teaspoon salt
In a separate bowl or stand mixer, beat together the softened butter, granulated sugar, and brown sugar on medium speed until light and fluffy, 3 minutes. Add in peanut butter and mix until well combined. Add in vanilla and eggs, one at a time, scraping down the bowl after each addition.
1 cup butter, 1 cup granulated sugar, 1 cup light brown sugar, 1 cup peanut butter, 2 teaspoon vanilla extract, 2 large eggs