Melt butter in a heavy kettle. Stir in the cabbage and 3 Tbsp. vinegar. Add 1/2 tsp. salt and a little pepper. Reduce heat to low and cover kettle. Stir often, and add more butter and vinegar if it looks like the cabbage may scorch. Cook until very tender; about 45 minutes. Stir in about a half of a bottle of beer and continue cooking for 10 more minutes. Serve with boiled potatoes and corned beef.