Heat 1 teaspoon of olive oil or butter in a large Dutch oven. Brown bratwurst sausages until deep golden brown. Remove to a platter. to the drippings, add the remaining teaspoon of olive oil or butter and the sweet onion rings. Toss the onions to coat with the oil. Cook, stirring often, until onions are limp and golden but not brown. Return the bratwurst to the onions and add the beer. Cook over medium heat until beer has cooked down to a syrup, about 12 to 15 minutes. Bratwurst may be served on buns with onions or as an entree.