In a large mixing bowl, use an electric mixer to beat butter and sugars until light and fluffy.

Add eggs and vanilla extract and beat until completely combined.

In a separate medium-sized mixing bowl, whisk together the flour, cocoa, baking powder, and salt.

Gradually add dry ingredients to wet, stirring until completely combined.

Cover bowl with plastic wrap and chill in the refrigerator for at least 4 hours (I usually chill mine overnight).

After the dough has chilled, preheat oven to 350F (175C) and line several baking sheets with parchment paper. Set aside.

Scoop dough into 1 ½ Tablespoon-sized balls and roll into a smooth ball with the palms of your hands, then roll through granulated sugar until completely coated. Transfer to a baking sheet, spacing cookies at least 2” apart and bake in center rack of 350F (175C) oven for 10-12 minutes. Meanwhile, ensure your marshmallows are prepared (cut in half).

Immediately after removing cookies from the oven, carefully press half a marshmallow directly into the center of the cookie (sticky side down). Allow cookies to cool on baking sheet for several minutes before carefully transferring to a cooling rack to cool completely before topping with chocolate.

Chocolate topping: Combine chocolate and heavy cream in a small microwave-safe bowl. Heat in the microwave for 25 seconds, stir well, and heat again for 25 seconds longer, if needed. Whisk well until mixture is completely smooth. Let cool slightly at room temperature.

Drizzle chocolate topping over the tops of the cookies. Allow ganache to set before serving.