In 3-quart saucepan, melt 1/2 cup chocolate chips and 1/2 cup butter over low heat, stirring constantly; remove from heat. Cool completely. Stir in brown sugar, eggs, 2 tablespoons liqueur and the vanilla with whisk. Stir in flour, cocoa and salt. Spread evenly in pan. Bake 20 minutes or until centre is set. Cool completely.