Heat half the butter in a large, heavy skillet over high heat and brown the beef in small batches until browned on all sides, transferring them to a large, heavy pot as they are done.
4 tbsp butter
Add the remaining butter to the same skillet and saute the onions until nicely browned, about 20 minutes.
3 large onions
Transfer the onions to the pot with the beef.
Deglaze the skillet with the beer, scraping up all the brown bits on the bottom of the pan, and add the beer to the pot.
3 cups dark beer
Stir in the thyme and bay leaf and bring to a boil over high heat.
1 tsp dried thyme, 2 whole bay leaves
Reduce the heat and simmer covered until the meat is very tender, 1 1/2 to 2 hours.
Stir in the currant jelly and vinegar immediately before serving.