This recipe is heavily adapted from Peanut Butter Chocolate Ganache Sandwich Cookies from Two Peas & Their Pod
Make the cookies: stir together flour, baking powder, baking soda, and salt. Set aside. Cream the butter with the two sugars, and then cream in the peanut butter. Stir in the eggs.
2. Chill the dough at least 4 hours, or overnight. Roll into 18 g balls, and place on baking sheet. Press the balls with the back of a fork to create a criss-cross pattern on the tops. Chill dough balls while preheating oven to 350 degrees (or while previous tray is baking). Bake for 7 minutes, 40 seconds; turn tray, bake for 2 minutes. Cool on wire rack.
3. Make the peanut butter frosting by adding all of the ingredients to a mixer in the order listed, and beating until well combined after each addition of sugar, and then until fluffy.
4. To make the chocolate ganache, heat the heavy cream in the microwave just until very warm (for us, that was 25 seconds). Pour over chocolate chips in a heavy bowl. Let sit 1 minute, then stir until smooth. Melt the butter in a separate bowl, and stir in the cocoa until smooth. Combine the two chocolates. Allow to cool to room temperature.
5. To assemble the cookies, place 8g of ganache (roughly 1/2 Tbsp) on one cookie, and 16g of peanut butter frosting on another cookie. Press the two cookies gently together.
Cookies will be good in the freezer for up to a year, but will be at their best quality if used within 4 months of freezing.