Classic French Onion Soup at Home

This is the dish onion season exists for: a mountain of cheap onions — a kilo and a half, minimum — stirred for a full hour until the sugars turn them jam-deep gold, while a slow cooker quietly builds a clear beef broth from seared meat, browned vegetables and an onion left in its skin for color. Wine, soy and Worcestershire sharpen the onions; the two hours meet in one pot with a last piece of butter. On top, the part restaurants charge for: thick baguette slices fried firm, buried under a heavy mozzarella lid that grills into a pulling, golden crust. It fed Paris market porters at dawn for pocket change, and it still costs about three dollars a bowl to make.