These are delicious! Be prepared, one is probably not enough! I found this recipe on loveveggiesandyoga.com. On their website they have step by step how to make everything about this from scratch (ex:brownie mix and frosting)
I took the semi-homemade approach. This recipe makes 24 brownies.
1- 7oz. jar marshmallow fluff
1/8 tsp. mint extract
8 drops of green food coloring
1 box of brownie mix
1 - 17oz. package of mint oreo cookies, hand crumbled
3/4 cup white chocolate chips, melted
1 cup vanilla frosting
Preheat oven to 350 degrees. Spray a 9x13 pan with cooking spray. In a medium bowl, stir together marshmallow fluff, mint extract and 4 drops of green food coloring or until you achieve a light green minty color. In a separate larger bowl, prepare brownie mix as directed on the box, using water, oil, eggs and fold in 10 hand crumbled oreos.
Spread brownie batter in prepared pan. Drop about 1/2 cup of green minty marshmallow mix onto brownie batter and reserve the remainder.
Gently pull a table knife through the batter in S-shape curves for a swirled design.
Bake for 23-25 mins, bake until brownies are set. Taking care not to over bake. Cool completely about 1 hour. While brownies are cooling in a small bowl, take 1 cup of store bought vanilla frosting and stir it till it's fluffy.
In a small microwave-safe bowl, melt white chocolate chips. (Microwave on high for 30 seconds; stir and microwave it 30 seconds longer; stir until smooth, taking care not to scorch it as white chocolate scorches easily.) Add the melted white chocolate to the vanilla frosting and then add it all to the reserved green minty marshmallow mixture. Stir in 4 more drops of green food coloring to keep it a light green color. Spread it over the cooled brownies.
Sprinkle with 18 hand crumbled oreos, slightly pressing them into the green minty layer. Allow top layer to set fully before slicing and serving. I waited 3 hours before slicing mine. You can store these in the refrigerator in an airtight container or store them in your freezer for up to 3 months. PS - Mine didn't last long enough to store! They were all gone in two days!