Preheat the oven to 350°F. Lightly grease a 24-cup mini muffin pan.

In a large mixing bowl, beat the butter, brown sugar, and granulated sugar until light and creamy, about 2 minutes. Add the egg, vanilla extract, and peppermint extract and beat until well combined. In a separate bowl, whisk together the Bob’s Red Mill Gluten Free 1-to-1 Baking Flour, cocoa powder, baking soda, and salt. Gradually add the dry ingredients to the butter mixture and mix just until combined. Fold in the ½ cup chocolate chips.

Divide the dough evenly among the 24 mini muffin cups, using about 1 tablespoon of dough per cup. Roll each portion lightly between your hands and place it in the pan. Bake for 10–12 minutes, or until the edges are set and the centers still look slightly soft. Do not over-bake.

Immediately after removing the pan from the oven, use the rounded end of a wooden spoon or a small measuring spoon to gently press a deep indentation into the center of each cookie. Be careful not to press all the way through. Let the cookie cups cool in the pan for 10 minutes, then transfer them to a wire rack to cool completely.

Place the ¾ cup chocolate chips in a heatproof bowl. Heat the heavy cream in a small saucepan over medium heat just until steaming; do not boil. Pour the cream over the chocolate and let stand for 2 minutes. Stir until smooth, then stir in the peppermint extract and salt.

Spoon about 1 teaspoon of the peppermint chocolate filling into each cookie cup. Let the filling sit for 5–10 minutes so it begins to thicken slightly. Place 2–3 mini marshmallows on top of each cookie cup, gently pressing them into the soft chocolate filling.

Drizzle the melted chocolate over the cookie cups. Sprinkle with crushed peppermint candies and, if using, sprinkles. Let the cookie cups stand at room temperature for about 20 minutes, or refrigerate for 10 minutes, until the chocolate is set.