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

2. Melt the unsalted butter and let it cool slightly, then whisk together with the granulated sugar until glossy.

3. Add the eggs one at a time, mixing gently, then stir in the vanilla extract and sourdough discard until smooth.

4. In a separate bowl, sift together the flour, cocoa powder, and hot cocoa mix.

5. Gradually fold the dry ingredients into the wet mixture until just combined, being careful not to overmix.

6. Fold in chocolate chips if using, then pour the batter into the prepared pan and spread evenly.

7. Bake for 28–32 minutes, or until the top is crackly and a toothpick inserted into the center comes out with moist crumbs.

8. Let the brownies cool in the pan on a wire rack, then spread marshmallow cream on top or sprinkle with mini marshmallows and toast until golden.

9. Allow the brownies to set before lifting out with the parchment overhang and slicing into squares.

10. Serve warm or at room temperature with a mug of hot cocoa or milk.