Prick each sausage a half-dozen times with a needle or pin stuck in a cork. Arrange the onion slices on the bottom of a sauté pan just large enough to hold all the sausages. Place the sausages on top and add beer and water to cover (the ratio should be about 3 parts beer to 1 part water). Place the pan over medium heat and gradually bring the liquid to a simmer, not a ra