Heat fat in 12-inch, deep skillet over medium heat. Add onions and sugar, stir well to coat with fat. Saut onions, stirring frequently, for 10 minutes, or until starting

to turn golden brown. Add beer, scraping up any browned bits from bottom of pan. Add bay leaves, lower heat and simmer for about 10 minutes. Stir mustard into onions, remove from heat and set aside, discarding bay leaves.

Grill bratwurst over medium-hot fire, turning to brown evenly, until nicely browned and internal temperature reaches 160 degrees F. on an instant-read meat thermometer. Remove from grill and add to skillet with onions. Over medium heat, cook and stir until sauce becomes syrupy. Serve bratwurst in rolls, generously smothered with mustardy onions.