Bake the steaks with a part of the butter in the oven. Slice the onions into thin strips and saute them in the remaining butter until golden.
Lay out half of the sauteed onions at the bottom of a wide pot. Arrange the steaks on top of them and cover with the remaining onions.
Sprinkle with black pepper and salt, pour on the beer. Cover the pot and leave to cook on low heat until the steaks soften.