Preheat your oven to 350°F (175°C). Grease your 9x13 inch baking pan or line it with parchment paper for easy removal.
In a medium saucepan over low heat, melt the butter and bittersweet dark chocolate together, stirring constantly until smooth. Remove from heat and let it cool slightly.
In a large mixing bowl, whisk together the granulated sugar and the melted chocolate mixture until well combined. Add in the eggs, one at a time, mixing after each addition. Stir in the vanilla extract.
In another bowl, sift together the cocoa powder, flour, baking powder, and salt. Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to over-mix.
Pour the brownie batter into the prepared baking pan, spreading it evenly. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Remove from the oven and let it cool completely in the pan on a wire rack.
In a mixing bowl, beat the softened butter until creamy. Gradually add the powdered sugar, mixing until well combined. Add the peppermint extract, vanilla extract, and a splash of milk if needed for consistency. If desired, add a few drops of green food coloring to achieve a lovely minty hue.
Once the brownies are completely cool, spread the mint frosting evenly over the top. Place the Mint Truffle Hershey's Kisses on top of the frosting, pressing them gently in.
Cut the brownies into bite-sized squares or rectangles. If you have extra Mint Truffle Kisses, feel free to use them as additional garnish! Enjoy your Mint Brownie Bites with friends and family.