01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, allowing overhang for easy removal.
02 - Melt butter in microwave-safe bowl. Stir in sugar, eggs, and vanilla extract until fully combined.
03 - Add cocoa powder, flour, salt, and baking powder to wet mixture. Stir gently until just combined, avoiding overmixing.
04 - Pour batter into prepared pan and smooth surface. Bake 25 to 30 minutes or until toothpick inserted comes out with moist crumbs.
05 - Remove from oven and cool completely in pan before adding topping.
06 - Melt white chocolate chips in a heatproof bowl over simmering water or microwave in short intervals, stirring frequently.
07 - Stir peppermint extract into melted white chocolate until evenly incorporated.
08 - Spread melted white chocolate evenly over cooled brownies. Optionally, melt semi-sweet chocolate and drizzle or marble on top.
09 - Immediately sprinkle crushed peppermint candies over topping and gently press to adhere.
10 - Allow brownies to set at room temperature or refrigerate until topping is firm. Lift from pan using parchment, cut into 16 squares, and serve.