Preheat your oven to 350°F (177°C) and lightly coat a 9-inch springform pan with non-stick spray.

In a medium bowl, whisk together the flour, baking soda, and salt until well combined.

In a stand mixer, beat together butter, peanut butter, brown sugar, and granulated sugar until light and fluffy, about 3-4 minutes. Add the egg and vanilla extract, mixing until incorporated.

Gradually add the dry ingredients to the wet mixture, mixing just until combined. Fold in peanut butter cups.

Spread the cookie dough evenly in the pan and bake for 20-25 minutes, or until edges are browned and a toothpick comes out clean.

Once baked, let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Prepare frosting by beating softened butter until smooth, then gradually add powdered sugar, cocoa powder, and heavy cream until fluffy.

Once cooled, frost the top of the cake evenly, adding extra mini peanut butter cups on top if desired.