Preheat the oven to 325 degrees. Grease a 13-by-9-inch pan. In the large bowl of an electric mixer, cream the butter. Add the eggs, one at a time, beating well after each addition. Add the Double-Fudge Brownie Mix, and continue to beat the mixture until it is smooth. Spread the mixture into the greased pan, and bake for 40 to 50 minutes.