01 -
Heat your oven to 350ºF. Want thick treats? Coat a 9x9" dish with cooking spray or add parchment paper. For thinner squares, grab a 9x13" dish instead.
02 -
Follow the box directions to make your brownie mix. Pour it into your dish and bake about 30 minutes until nearly done. Don't leave them in too long.
03 -
Take brownies out and scatter the 2 cups of mini marshmallows all over the top. Pop back in the oven for 3 more minutes until they swell up. Pull them out and let them cool down.
04 -
Mix the soft butter, confectioners' sugar, cocoa powder, milk, and vanilla in a big bowl. Use your mixer until it's all blended. Add extra milk or sugar to get the right creamy texture.
05 -
Drop spoonfuls of your chocolate frosting onto the cooled marshmallow layer. Spread it carefully across the top. Cut into 5x4 pieces using a plastic knife.