In a Dutch oven over medium heat, add the oil, onions, peppercorns and bay leaf. Add the sausage. Saute until the sausages begin to brown and the onions soften, about 5 minutes. Add the ale. Be sure to turn the sausages over and continue cooking, another 2 minutes. Cook on low for 20 minutes. Serve the bratwurst with the braised onions on crusty rolls with spicy mustard.