Preheat your oven to 350°F (175°C).
Grease a 9x13 inch baking pan with butter or cooking spray.
Melt the unsalted butter in a large mixing bowl. Add the granulated sugar and stir until well combined. Then, add the eggs one at a time, mixing thoroughly after each addition. Stir in the vanilla and peppermint extracts.
In a separate bowl, sift together the flour, cocoa powder, salt, and baking powder. Gradually add this dry mixture to the wet ingredients, stirring until just combined. Fold in the semi-sweet chocolate chips.
Pour the brownie batter into the prepared baking pan, spreading it evenly. Sprinkle the crushed peppermint candies on top.
Bake for 25-30 minutes. Check for doneness with a toothpick; it should come out with a few moist crumbs.
Let the brownies cool in the pan for at least 15 minutes before cutting into squares.