Flanders, a region in the southwestern part of the Low Countries (now divided between Belgium, France, and the Netherlands), has long been known for its fine beers. Cooking with beer is also a tradition there, and this stew, beef braised with thick slices of onion in Flemish-style dark beer, is an outstanding example. Serve it with a slice of hearty bread to soak up the flavorful, savory juices.