Preheat oven to 350°F. Grease approximately 15 wells of a mini muffin pan with cooking spray and set aside.
In a large bowl, combine flour, cornstarch, baking powder, salt, and cocoa powder.
In a separate bowl, cream together butter, coconut oil, and sugars. Add eggs and vanilla extract and mix until combined.
Pour wet ingredients into dry and mix until all ingredients are integrated. Using hands, shape dough into small rounded shapes that cover the bottom and sides of the mini muffin wells. Press mixture into wells, creating a cookie cup that will hold the filling. Take care to reserve enough mixture for covering the cookies.
In a separate bowl, mix together peanut butter, ¼ cup granulated sugar, and ¼ teaspoon vanilla extract with a hand mixer until peanut butter starts to develop a whipped consistency. Using a spatula, transfer filling mixture into a plastic bag and seal.
Snip a corner of the plastic bag, and pipe PB mixture into the cookie cups. Press piping tip into dollop to ensure there are no air bubbles.
Shape remaining dough into rounds and press on top of cookie cups, paying extra attention to pressing around the perimeter to seal the seams of the cookie cups. Repeat until all cookie cups are covered.
Bake for 12-13 minutes, or until tops of cookie cups give slightly when pressed. Remove from oven and let cool in muffin pan for 5 minutes. Remove cups and let cool completely on a wire rack.
Nutritional information is provided as an estimate. As it can vary due to many factors (brands used, quantities, etc.), we cannot guarantee its accuracy.