1. Preheat oven to 350°F (175°C) and line an 8×8-inch baking pan with parchment paper.

2. In a large bowl whisk melted butter, granulated sugar, and brown sugar until thick and shiny.

3. Add sourdough starter and whisk until fully combined.

4. Beat in eggs one at a time, then stir in vanilla and peppermint extracts.

5. Sift in cocoa powder, espresso powder, and salt, folding gently until no streaks remain.

6. Fold in chocolate chunks and half of the crushed candy canes.

7. Pour batter into prepared pan and smooth the top.

8. Bake for 28–32 minutes until edges are set and a toothpick yields moist crumbs.

9. Cool in pan on a rack for 30–45 minutes before lifting out with parchment overhang.

10. Prepare mocha glaze by whisking melted dark chocolate, brewed espresso, and butter, then drizzle over cooled brownies.

11. Sprinkle remaining crushed candy canes over glaze and allow to set before slicing.