1. Line a 9×13 inch pan with parchment paper and preheat the oven to 350°F (175°C).

2. Melt dark chocolate and butter in a heatproof bowl over simmering water, stirring until smooth. Remove from heat and let cool slightly.

3. Whisk granulated and brown sugar into the melted chocolate until fully combined.

4. Beat in eggs one at a time, then stir in vanilla extract until the batter is glossy.

5. Sift together flour, cocoa powder, and salt, then fold gently into the chocolate mixture until just combined.

6. Pour batter into the prepared pan, smooth the top, and bake for 28–32 minutes until a toothpick yields moist crumbs.

7. Let brownies cool completely in the pan on a wire rack, about 60 minutes.

8. Melt white chocolate over simmering water, stir in peppermint extract, then spread evenly over cooled brownies.

9. Sprinkle crushed candy canes over the white chocolate layer and drizzle with melted dark chocolate if desired.

10. Refrigerate for 30–45 minutes until the topping is firm, then lift out with parchment overhang and cut into squares.