Preheat the oven to 350°F and line an 8x8 inch pan with parchment, leaving an overhang on two sides.

Whisk the melted butter and granulated sugar together, then whisk in the eggs and vanilla until smooth.

Stir in the cocoa powder, flour, and salt just until combined, do not overmix or the brownies turn tough.

Pour the batter into the pan and smooth the top, then bake for 22 to 25 minutes, until a toothpick inserted in the center comes out with a few moist crumbs.

Cool the brownies completely in the pan, at least 1 hour, before frosting.

Beat the powdered sugar, softened butter, milk, peppermint extract, and food coloring if using until smooth and spreadable, then spread evenly over the cooled brownies.

Chill the frosted brownies for 20 minutes, until the frosting firms up slightly.

Heat the chocolate chips and cream together in short bursts in the microwave, stirring between each, until smooth and pourable, then pour over the chilled frosting and tilt the pan to spread it evenly.

Chill again for 15 minutes, until the ganache sets, then lift out using the parchment overhang and cut into 16 bars with a warm, clean knife.