Begin by preparing the cookies. Line a baking sheet with parchment paper and set aside. Preheat oven to 375 degrees.
In a large bowl, cream together butter, peanut butter, both sugars and eggs.
Once all ingredients are creamed together, add dry ingredients: flour, baking powder, salt and baking soda.
Once the ingredients are well-combined and have formed a cookie dough, roll into 1 inch balls and place on the lined baking sheet, about 1 ½ to 2 inches apart from each other. (To make 24 cookies, you will need to bake in batches. Normally, 12 cookies can fit on a standard-sized cookie sheet).
You will have leftover cookie dough, be sure to wrap in plastic and refrigerate for up to 7 days for later use.
Flatten each cookie with a fork, using a crisscross pattern. Bake for 8-10 minutes. Allow to cool completely before adding the filling.
To make the sandwich filling, add all ingredients to a large bowl and use an electric mixer to mix all of it together.
Flip over half of the cookies and use a piping bag to frost them with the peanut butter filling. Sandwich each one with an empty cookie.