To make the brownies, preheat oven to 350 F. Grease and flour a 9 x 13 inch pan. Melt the butter in a large microwave safe bowl. Whisk in the oil, sugar, eggs, vanilla and mint extracts. Beat in the cocoa, flour, salt and baking powder. Spread half the batter into the prepared pan, layer on 24 whole mint oreos and spread the second half of the batter on half. Bake for 25-30 minutes or until an inserted toothpick comes out with a few crumbs. Let cool completely.
To make the mint buttercream layer, beat the butter in a stand mixer for 1-2 minutes, beat in the powdered sugar. Add enough of the milk or cream to be a spreadable consistency and the mint extract to your tastes. Spread on top of cooled brownies.
Gently crush the remaining oreos in the package and sprinkle on top of the frosted brownies.
to make the fudge drizzle, melt the butter in a medium microwave safe bowl. Stir in the cocoa powder, corn syrup, powdered sugar, and enough milk or heavy cream to make a smooth consistency. Microwave to 20 seconds and stir. Drizzle on top of cooled brownies. I put mine into a ziploc bag and cut the corner off for a more controlled drizzle. Let cool and cut into bars.