Preheat your oven to 350°F (175°C). Lightly grease your baking pan or line it with parchment paper for easy removal later.
Place butter and unsweetened chocolate in a saucepan over low heat. Stir constantly until fully melted and smooth, then remove from heat.
Stir sugar into the warm chocolate mixture, followed by eggs and vanilla. Mix gently until everything is fully combined and glossy.
In a separate bowl, whisk together flour, baking powder, and salt. This ensures even distribution and prevents clumping.
Add dry ingredients to the chocolate mixture and stir until just combined. Fold in chopped mint chocolate and crushed peppermint candy.
Pour batter into the prepared pan and spread evenly. Bake for 25–30 minutes until the edges are set and the center is slightly soft.
Let the brownies cool completely in the pan. Cooling helps them firm up and makes slicing cleaner and easier.