Preheat your oven to 350°F (175°C).
Cream together the softened unsalted butter, granulated sugar, and light brown sugar using an electric mixer until light and fluffy.
Add the egg and vanilla extract to the mixture and beat until fully incorporated.
In a separate bowl, whisk together the cake flour, cornstarch, baking powder, baking soda, and a pinch of salt. Gradually add to the wet mixture until just combined.
Fold in the Reese’s Peanut Butter Chips gently.
Scoop rounded balls of dough onto a lined baking sheet, spacing them about 2 inches apart. Bake for 10-12 minutes until edges are golden.
Cool the cookies on the baking sheet for 5 minutes before transferring to a wire rack.
Beat together the softened unsalted butter and creamy peanut butter for the frosting until smooth. Gradually add confectioners sugar and a pinch of salt, adjusting consistency with cream or milk.
Frost each cooled cookie generously with the peanut butter frosting and sprinkle with chocolate sprinkles if desired.
Serve and enjoy!