Preheat your oven to 350°F and grease a 9x13-inch baking pan.

In a large mixing bowl, melt the butter and stir in the sugar and cocoa powder until smooth. Add the vanilla extract and eggs, one at a time, mixing well after each addition. Gradually fold in the flour and salt until just combined.

Pour the brownie batter into the prepared pan and spread evenly. Bake for 25-30 minutes or until a toothpick inserted into the center comes out with a few moist crumbs. Allow to cool completely.

In a medium mixing bowl, beat the softened butter until creamy. Gradually add powdered sugar, alternating with milk, and beat until smooth. Stir in peppermint extract and food coloring until well combined.

Once brownies are cool, spread the mint frosting evenly over the top using a spatula. Let the frosting set for 15 minutes before cutting.

Use a sharp knife to cut the brownies into squares or rectangles. Serve at room temperature.

Store the brownies in an airtight container at room temperature for up to 3 days or refrigerate for up to a week.

Wrap individual slices in plastic wrap and freeze in a freezer-safe bag for up to 3 months. Thaw at room temperature before serving.