Soupe à l'Oignon Gratinée — French Onion Soup

Soupe à l'oignon gratinée is perhaps the most beloved of all French soups — a deep, mahogany broth of slowly caramelised onions, ladled into ovenproof crocks, topped with croûtons and a generous mantle of Gruyère, and gratinéed under fierce heat until the cheese forms a bubbling, golden-brown crust that bridges from rim to rim. Its origins lie in the markets of Les Halles, where it sustained porters and merchants through long predawn hours, and its power derives entirely from one thing: the quality and depth of the onion caramelisation. Slice 1kg of yellow onions (not sweet onions — you need the sulphurous pungency that cooking transforms) into thin half-moons. Melt 60g of butter in a heavy-bottomed pot over medium heat, add the onions with a generous pinch of salt, and begin the slow journey. The first 15 minutes will steam and soften the onions as they release moisture. Once dry, reduce heat to medium-low and cook for 45-60 minutes, stirring every 5-7 minutes, scraping the fond that forms on the bottom and dissolving it back into the onions. This fond — the Maillard reaction products that cling to the pot — is the soul of the soup. Deglaze periodically with small splashes of water or dry white wine to dissolve stubborn fond. The onions should progress from translucent to golden to deep amber to a rich, dark mahogany. There are no shortcuts — sugar caramelises on its own schedule, and impatience produces bitter, burnt onions instead of the sweet, complex depth you seek. Deglaze finally with 150ml of dry white wine or cognac, then add 1.5 litres of dark beef stock (never chicken — you need the colour and body) and a bouquet garni. Simmer 20 minutes. Season with salt, pepper, and a splash of sherry vinegar to sharpen the sweetness. Ladle into ovenproof crocks, float thick croûtons of toasted baguette, cover generously with grated Comté or Gruyère (100g per bowl), and gratinée under a blazing grill until the cheese bubbles fiercely, browns in spots, and seals the bowl in a molten cap. The first spoonful should break through cheese into deeply flavoured, onion-rich broth — sweet, savoury, sharp, and comforting in equal measure.