With the oven rack in its lowest position, pre-heat oven to 325°F. Remove and discard neck and giblets from turkey. Rinse turkey inside and out with cold water; pat dry with paper towels and fold wings in behind. In shallow roasting pan, place turkey, breast side up.
In medium bowl, stir together butter, mustard, rosemary, salt, pepper and ¾ of the can of beer. Drink remaining beer. Microwave uncovered on High 1 to 1 1/2 minutes, stirring after 30 seconds, until well mixed. Brush about 1/3 of mixture evenly over surface of turkey. Fasten drumsticks together with cotton string. Optional: Add Back Lakes Stuffing to bird prior to cooking (see below for recipe).
Roast uncovered 2 1/2 to 3 hours, brushing with additional beer mixture and pan juices every 30 minutes. Turkey is done when thermometer reads 165°F and drumsticks move easily when lifted or twisted. If necessary, cover turkey breast with heavy-duty foil during last 1 hour 30 minutes to 2 hours of baking to prevent excess browning.
Let stand 15 to 20 minutes for easier carving. Serves up to 15 people.
Optional: Add turkey drippings into a saucepan, and heat until boiling. In small cup, stir together cold water and flour until smooth, add into boiling drippings. Continue stirring 2 to 3 minutes longer or until gravy is thickened and bubbly.