Preheat the oven to 350 degrees F. Line a 9x13-inch baking pan with foil- enough to hang over two edges. Spray lightly with cooking spray.
Prepare the brownies: In a microwave-safe bowl, melt the butter and chocolate in the microwave-- 30-second bursts, stirring between bursts, until melted and smooth. Whisk in the cocoa powder until completely incorporated. Add sugar, brown sugar, vanilla and salt, whisking to combine. Whisk in the eggs, one at a time, until completely mixed through. Gently whisk in the flour just until incorporated and no more flour is visible. The batter will be thick.
Prepare the mint fudge: In a separate bowl, heat the white chocolate and condensed milk in the microwave in 30-second intervals, stirring between each burst, until melted and smooth. Add mint and food coloring, and stir to combine.
Assemble the brownies: Spread half of the brownie batter evenly into the prepared pan, and carefully spread the fudge on top. Gently spread the remaining brownie batter evenly over the fudge. Sprinkle 1 cup of the chopped mints over the top.
Bake for 30 to 35 minutes or until the brownies are set and the edges start to slightly pull away from the pan. We sprinkled a few more chopped mints on top as soon as they came out of the oven. Allow to cool, then refrigerate until completely set, at least 2 hours.