Start by preheating your oven to 350°F (175°C). Prepare a 9x13-inch baking pan by greasing it lightly and lining it with parchment paper, allowing some overhang to facilitate easy removal later.
In a large saucepan set over medium heat, melt the unsalted butter until it is completely liquid. Once melted, remove the saucepan from the heat and add the granulated sugar and packed brown sugar. Stir continuously until the mixture is well combined and smooth.
Allow the mixture to cool for a few minutes to avoid cooking the eggs. Then, whisk in the eggs one at a time, ensuring each egg is fully incorporated before adding the next. Stir in the vanilla extract.
In a separate mixing bowl, sift together the all-purpose flour, unsweetened cocoa powder, baking powder, and salt. Gradually fold the dry ingredients into the wet mixture using a spatula, being careful not to overmix; just combine until no dry flour remains.
Gently fold in the cooled brewed coffee and peppermint extract, followed by the semi-sweet chocolate chips, ensuring they are evenly distributed throughout the batter.
Pour the brownie batter into the prepared baking pan, using a spatula to spread it out evenly across the surface.
Place the pan in the preheated oven and bake for 25-30 minutes. Check for doneness by inserting a toothpick into the center; it should come out with a few moist crumbs attached.
After baking, allow the brownies to cool in the pan for about 10 minutes. Once slightly cooled, lift them out using the parchment overhang and place them on a wire rack to cool completely.
Once fully cooled, use a sharp knife to cut the brownies into squares. Serve topped with a dollop of whipped cream if desired, and garnish each piece with fresh mint leaves for a refreshing finish.
Notes
For best results, allow brownies to cool completely before cutting.