1 box of brownie mix plus the ingredients listed on the package
1/3 c marshmallow fluff
For the frosting
1 cup (2 sticks) salted butter, softened
1 ½ cups marshmallow fluff (about one 7 oz jar)
2 cups powdered sugar
1 tsp vanilla extract
1–2 tbsp heavy cream, as needed
Green food coloring
For the decorations
Lucky Charms marshmallows
Edible gold flakes
Instructions
Preheat the oven to 350 degrees and line a 9” square baking dish with parchment paper and spray it with baking spray.
Prepare the brownie mix according to the package instructions. Pour the batter into the prepared pan, smoothing it into an even layer drop dollops of the fluff onto the brownie batter and gently swirl it in with a knife. It doesn’t have to be perfect because it’ll bake in to the brownies.
Bake the brownies according to the package and then let them cool completely. I love to transfer them to the fridge for an hour or two because it makes them extra fudgy!
Meanwhile, in a large mixing bowl, beat the softened butter with an electric mixer on medium speed for about 2 minutes, until smooth and fluffy.
Mix in the marshmallow fluff and continue beating until well incorporated.
Add powdered sugar, one cup at a time, mixing on low speed at first, then increasing to medium-high. Scrape down the sides of the bowl as needed.
Mix in the vanilla extract and a food coloring until you don’t see any streaks of color. If the frosting is too thick, add 1-2 tbsp of heavy cream or milk, a little at a time, until it reaches your desired consistency.
Beat on high speed for another minute or two until light, fluffy, and smooth.
Spread the frosting onto the cooled brownies. If you don’t want to use it all, set the remaining amount aside for another use. Top with gold flakes and Lucky Charms marshmallows and cut into squares. Enjoy!