1. Preheat & Prep: Preheat oven to 350°F (175°C). Grease an 8-inch round cake pan (or heart-shaped pan) and line the bottom with parchment paper.

2. Whisk Dry Ingredients: In a small mixing bowl, combine the gluten free flour, cocoa powder, baking soda, and salt. Whisk well to break up any cocoa lumps.

3. Mix Butter & Sugars: In a large mixing bowl, whisk together the melted butter, granulated sugar, and brown sugar for about 30 seconds until evenly combined.

4. Add Wet Ingredients: Add the egg yolks and vanilla extract to the butter-sugar mixture. Whisk again until smooth and combined.

5. Combine Batter: Add the dry ingredients to the wet ingredients. Stir with a spatula until the flour is fully incorporated and no streaks remain.

6. Add Chocolate: Fold in the chocolate chips until evenly distributed throughout the dough.

7. Bake: Spread the dough into the prepared pan, using an offset spatula or your hands to press it into an even layer. Bake for 18–22 minutes. The center should still look slightly soft but the edges will be set.

8. Cool: Allow the cookie cake to cool completely in the pan before removing or frosting.

9. Make Frosting: Beat the softened butter until creamy. Gradually add the powdered sugar and vanilla. Add milk one tablespoon at a time until fluffy and spreadable.

10. Decorate: Pipe or spread the buttercream around the edges (or all over) and top with sprinkles if desired.