FOR THE BROWNIES: Preheat the oven to 350º.
Spray or grease an 8x8-inch pan or line it with parchment paper.
In a large bowl mix all the brownie ingredients together, (the package of dry brownie mix, Irish Cream liqueur, oil, egg, and butter.) You are following my ingredients, not what is on the box.
Pour the batter into the prepared pan.
Bake at 350º for 30-35 minutes. The center should be slightly firm to the touch, not completely firm.
Cool the pan on a wire rack for 30 minutes.
FOR THE FROSTING: Beat all the frosting ingredients together. Start the mixer on low speed, then increase it to medium. Beat until it is smooth and creamy.
Frost the cooled brownies.
Decorate with sprinkles if you wish.
Store the brownies covered at room temperature.