Preheat your oven to 350°F (175°C) and line a 9x13-inch baking pan with parchment paper, lightly greasing the sides.

In a large mixing bowl, combine melted butter with granulated and brown sugars, whisk until glossy and smooth.

Add eggs one at a time, whisking well after each addition, then stir in vanilla extract.

In a separate bowl, sift together flour, cocoa powder, baking powder, and salt. Fold this mix into the wet ingredients.

Pour the batter into the prepared pan and smooth the top. Bake for 25–30 minutes, until a toothpick comes out with a few moist crumbs.

Allow the brownies to cool completely on a wire rack for 30–45 minutes.

Prepare the mint frosting by beating softened butter until creamy, gradually adding sifted powdered sugar until fully incorporated.

Add heavy cream, peppermint extract, and vanilla extract. Beat until light and fluffy, adjusting food coloring to desired hue.

Spread the frosting evenly over the cooled brownies with an offset spatula.

Sprinkle crushed chocolate sandwich cookies over the frosted brownies and gently press red chocolate candies into the frosting.

Chill the decorated brownies in the refrigerator for 20–30 minutes to set the frosting, then slice into squares.