- FOR THE BARBECUED ONION RELISH:Heat oil in large saute pan over medium heat. Add onions, sugar and salt. Cover and cook until onions are wilted and very juicy, but not browned, stirring occasionally, about 30 minutes.
- Add chili powder, garlic and red pepper flakes; saute 4 minutes. Stir in barbecue sauce, beer, molasses, mustard, vinegar and soy sauce. Simmer uncovered until mixture thickens slightly, stirring occasionally, about 10 minutes. Cool to room temperature. Cover tightly and refrigerate at least 24 hours for flavors to develop.
- DO-AHEAD TIP:Relish can be prepared up to 1 week ahead. Keep refrigerated.
- FOR THE SANDWICHES:Prepare barbecue (medium heat) and position rack about 6 inches above heat source. Pierce sausages all over with tip of knife. Arrange sausages on rack. Cover and grill until outside is crisp and brown, and just cooked through, turning occasionally, about 15 minutes. Transfer to plate.
- Simmer relish over low heat. Lightly toast cut sides of buns on grill.
- Place bratwursts in buns and serve, allowing guests to add pickles, relish and cheese.
- NOTE:The ideal type bratwurst for this recipe is coarsely ground and uncooked. Fully-cooked, smooth-textured white "bratwurst," sometimes called weisswurst, can be substituted, but should be grilled just long enough to crisp them and heat them through.