4 (1 ounce) squares unsweetened chocolate
1/2 cup butter
3/4 cup packed brown sugar
3/4 cup white sugar
4 tablespoons brandy-based orange liqueur (such as Grand Marnier®)
1 teaspoon vanilla extract
1 teaspoon orange zest
3/4 cup all-purpose flour
1/8 teaspoon salt
1/2 cup semisweet chocolate chips
1/4 cup chopped walnuts (optional)
Chocolate icing for decorating (optional)
Preheat oven to 350 degrees F
Grease and lightly flour an 8 inch square baking pan.
Melt the chocolate and butter over low heat, in a medium saucepan. Stir until smooth. Remove from heat and cool slightly.
In a large bowl, beat sugars and eggs until light and fluffy (about 2 minutes with electric mixer). Add melted chocolate, 3 tablespoons of the Grand Marnier, vanilla and the orange peel, mixing until well blended. Mix in the flour, salt and chocolate chips (on low speed if using an electric mixer).
Pour batter into prepared pan. Smooth the top. Bake for 30-35 until sides look done and top feels firm. The toothpick test should come out clean but the center will jiggle and look undercooked.
Remove from oven and brush top with the remaining 1 tablespoon Grand Marnier. Cover pan with foil or plastic and cool completely.
Drizzle with the icing of choice if desired and walnuts for garnish.