Preheat your oven to 350°F. Grease a 12-cup mini muffin tin or line with mini muffin liners.
In a bowl, whisk together the gluten-free flour, cocoa powder, baking soda, and salt.
In a separate bowl, beat together the butter, granulated sweetener, and brown sugar until light and fluffy. Add the egg and vanilla extract, mixing well. Gradually mix the dry ingredients into the wet ingredients until well combined. The dough will be thick.
Divide the dough evenly among the prepared muffin cups, pressing gently to form a cup shape. Bake for 10-12 minutes or until set. Remove from the oven and immediately use a spoon to press down the center of each cookie cup to create a well. Allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.
For the filling, beat together the peanut butter, sweetener, heavy cream, and vanilla extract until smooth and creamy. Once the cookie cups are cool, spoon or pipe the peanut butter filling into the wells of each cookie cup. Refrigerate the cookie cups for at least 20 minutes to set the fi ling before serving.