1. Using a fork, prick each brat 4 times. Arrange in a shallow dish, pour over beet and allow to marinate for an hour.
2. Take a small bowl, add mustard. Add horseradish and beer and allow the mixture to stand for 20 minutes before being served.
3. Preheat the broiler.
4. Arrange drained bratwursts on rack on the broiler pan, keeping the broiler at 4 to 6 inches from the heat. Broil for about 2 to 3 minutes, allowing brats to turn brown. Turn the brats and continue to cook till the brat skin is brown as desired.
5. Meanwhile, place a large non-stick skillet on medium heat, melt butter and add rolls, as batches, and allow both sides to brown slightly.
6. Arrange brats and rolls on individual plates and serve with pickles and mustard sauce.