One 13x9 pan of brownies, baked, cooled and cut in half (line the pan with non-stick foil to make lifting the brownies out as easy as possible!)
For the glaze
10 ounces dark or bittersweet chocolate, chopped fine
1 cup heavy cream
1/4 cup light cane syrup (Karo light syrup)
4 tablespoons butter, softened
1/4 teaspoon peppermint extract
For the filling
12 tablespoons butter at room temperature
2 tablespoons heavy cream
1 teaspoon peppermint extract
1 1/2 cups confectioner’s sugar
Instructions
Make the glaze first so it has time to cool: Put the chopped chocolate in a medium sized mixing bowl. Stir the cream and the corn syrup in a small heavy pot over medium heat until it reaches a low boil.
Pour the hot cream mixture over the chopped chocolate and whisk until smooth. Add the 4 tablespoons butter and 1/4 teaspoon mint extract and whisk again until smooth. Cover and put in the fridge until it is spreadable, about 60 minutes.
When the glaze is set, make the filling: beat 12 tablespoons butter with 2 tablespoons cream and 1 teaspoon mint extract on medium until well-combined. Add confectioner’s sugar and beat on low until it is mixed in. Now rev the mixer up to high and beat until everything is nice and fluffy, about 3 minutes or so.
Time to assemble! Put the one brownie half bottom side down on a cooling rack that is place on a rimmed baking sheet. Spread all the filling evenly over it. Pop the other half on top, bottom side up (to give you a smoother spreading surface). Take 1 cup of the glaze and spread it in a thin layer over the sides and the top (if you have an offset spatula this is the time to break it out!).
Save a couple tablespoons of the remaining glaze and set aside. Put the rest in the microwave for a minute until it is melted. Pour it over the top of the cake, using a spatula to spread it along the top and to help it drip down the sides.
If you like, put the 2 tablespoons you saved into a ziplock bag, snip off a corner and pipe decorative squiggles over the top.
Refrigerate for at least 30 minutes, then transfer the cake onto a platter (I use two spatulas for this) and serve!