01 - Preheat grill to medium-high heat, approximately 400°F.
02 - Heat vegetable oil in a skillet over medium heat. Add sliced onions and cook, stirring frequently, until softened and golden brown, approximately 8 minutes.
03 - Add drained sauerkraut and caraway seeds (if using) to the skillet with onions. Stir and cook for an additional 3-4 minutes until heated through. Season with black pepper to taste.
04 - Place beef bratwursts on the preheated grill. Turn occasionally and cook for 12-15 minutes until evenly browned and fully cooked, reaching an internal temperature of 160°F.
05 - During the final 2 minutes of grilling, place buns cut-side down on the grill to lightly toast.
06 - Place a grilled bratwurst in each toasted bun. Top generously with warm sauerkraut-onion mixture. Add mustard, ketchup, and pickles as desired. Serve immediately.