Place bratwursts, beer, onion, peppercorns, and cloves in a 3 litre saucepan. Simmer for 20 minutes. Drain. Grill bratwursts 2 to 13 cm from charcoal about 10 minutes, until browned. Sprinkle with water to form a crisp skin. Serve in hard rolls with Dusseldorf style mustard.