Prepare your baking pan. Preheat your oven to 325°F (165°C). Line an 8-inch square pan with parchment paper, leaving some overhang for easy removal. Lightly grease the sides if needed.

Create the chocolate base. In a mixing bowl, combine the melted butter and brown sugar. Stir until the mixture looks glossy and smooth. Add the eggs one at a time, mixing gently after each addition. Stir in the peppermint extract for that signature holiday flavor.

Mix the dry ingredients. In a separate bowl, whisk together: flour, cocoa powder, espresso powder (if using), cornstarch, baking powder. Gradually fold the dry mixture into the wet ingredients. Mix just until a thick, uniform batter forms.

Add chocolate chips. Fold in the chocolate chips or chunks, reserving a small handful to scatter on top if desired.

Bake the brownies. Spread the batter evenly into the prepared pan and smooth the surface. Bake for about 28–30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs (not wet batter).

Cool completely. Allow the brownies to cool fully in the pan before adding frosting. This prevents the topping from melting and ensures clean layers.

Make the frosting. In a bowl, combine melted butter, cocoa powder, powdered sugar, and milk. Stir until smooth and spreadable. If the frosting feels too thick, add a small amount of milk gradually until it reaches the desired consistency.

Frost and decorate. Spread the frosting evenly over the cooled brownies. Immediately sprinkle crushed peppermint candy over the top for texture and a festive look.

Slice and serve. Cut into squares using a sharp knife. For clean edges, wipe the knife between cuts or dip it in warm water and dry it.