Preheat oven to 350 degrees. Grease muffin pan with cooking spray.

Melt chocolates, butter, and cocoa powder in microwave or in a double boiler; stirring often. When melted remove from heat and set aside to cool slightly.

Whisk sugar, eggs, vanilla, and salt together in a large bowl until well combined. Whisk in melted chocolate until smooth. Add in flour until well combined.

Use a small cookie scoop to pour batter into prepared pan (abut 3/4 of the way).

Bake for about 15 minutes or until toothpick in center comes out clean.

Immediately press marshmallows on top of brownies. Allow brownies to cool before removing from pan.

Melt white chocolate and pour into piping bag or use a spoon to drizzle chocolate on top of brownies. Allow chocolate to set before serving.