• Preheat the oven to 350°F. Line a 9x13-inch pan with parchment paper.
• In a medium mixing bowl stir the melted butter, sugar, and salt together.
• Add the cocoa powder and beat on low speed with a hand mixer until smooth and creamy.
• Add the eggs and beat on low speed until smooth and creamy.
• Beat in the flour and baking powder on low speed just until combined, don't overbeat.
• Scrape the batter into the pan and spread evenly from edge to edge. Bake 20 minutes. Cool.

Make the frosting:

• In a medium bowl beat the butter and sour cream together 2 - 3 minutes on medium speed until fluffy.
• Add the sugar and beat on low to start, once combined beat on medium speed 5 minutes, adding the milk if it seems dry or too thick.
• Beat in the peppermint extract and food coloring.
• Spread over the brownies and refrigerate 20 minutes for easier cutting.
• Cut into 20 squares with a chef's knife, wiping clean after each cut.
• Press a peppermint patty onto the top of each square.
• Store in a cool, dry place tightly covered 3 - 4 days.