Saute the onion and garlic  in butter until soft and transluscent. 
Sprinkle 3 +/- Tbs flour over onions, stirring & adding just until butter & juice are absorbed.
Slowly mix beef stock in, stirring & adding until all the flour is all thinned out. Watch for lumps.
Place onions, garlic ,beef stock, white wine, sherry, and Worcestershire sauce in crockpot.
Cover; cook on low for 6-8 hours.
Slice the French bread. Toast the slices.
To serve, place one slice in the bottom of a soup mug or bowl.
Top with shredded cheese. Pour soup over top.
Place in hot oven or under broiler if desired to melt the cheese more.