Wash the fresh mint and pat dry with a paper towel. In a small, thick bottom pan melt the butter over low to medium heat. Do not let it bubble.
Place the mint, leaves, stems and all into the melted butter. Remove the pan from the heat. Smash the mint, bruising the stems and leaves to release the flavor. Cover and set timer for 20-25 minutes.
While the mint is infusing into the butter, prep a 9x13 pan by lining it with foil or parchment paper. Preheat oven to 350 degrees F.
When the timer goes off, strain the butter from the mint into a large mixing bowl. Discard any large pieces of mint, the small flecks of mint are alright.
Add the sugar and vanilla to the butter, whisk until well blended. Add the eggs one at a time, whisking thoroughly after each egg. Using a spoon now instead of the whisk, add the cocoa and flour, stir to a uniform consistency. The batter will be very thick.
Scrape the batter into the 9x13 pan you prepared earlier and smooth out evenly. Bake for 30-35 minutes or until a toothpick inserted into the center comes out with moist crumbs but not wet batter.
Remove from the oven. Cool on cooling rack for 15 minutes, then lift out of pan with the foil or parchment paper liner and finish cooling on the cooling rack.
When completely cool sprinkle with powdered sugar by sifting it over top of brownies. Cut and enjoy!
