1Heat broiler. Split rolls lengthwise, cutting to but not through back of roll. Place rolls onto ungreased baking sheet. Broil 5 to 6 inches from heat until rolls are toasted (2 to 4 minutes).
2Meanwhile, heat bratwurst according to package directions. Spread 1-1/2 teaspoons mustard onto cut-sides of rolls.
3To assemble each sandwich, layer 1 slice cheese, 1 hot bratwurst and 1 tablespoon Frank's Kraut. Top each sandwich with 2 slices cheese.
4Continue broiling until heated through and cheese is melted (1 to 2 minutes)