Soupe à l'oignon gratinée

As tradition built it

Serves 4. About 1 hour 30 minutes, mostly unattended.

Ingredients

• 1 kg onions, thinly sliced
• 60 g butter
• 1.5 L good beef or veal stock
• 200 ml white wine
• 25 g flour
• 1/2 day-old baguette, sliced
• 150 g Gruyère or Comté, grated

Method

1. Melt the butter in a heavy pot and add the onions. Cook over medium, not high, heat, stirring occasionally rather than constantly, for a genuine 40 to 60 minutes, until deeply caramelised, dark gold-brown, not merely softened. This is the whole dish. Do not shortcut it.
2. Dust with flour, cook a further minute, then deglaze with the wine, scraping up anything stuck to the base.
3. Add the stock and simmer gently for at least 30 minutes.
4. Ladle into oven-safe bowls, float a slice of toasted baguette on top, cover generously with the grated Gruyère or Comté, and grill until blistered and golden.

What a modern chef changes

An onion extraction concentrated by cold, not heat, and a controlled caramelisation

Rungs 4 and 5

Method

1. Caramelise the onions sous vide. Bag the sliced onions with the butter and seal, then hold at 85°C for four hours. This gives a completely even caramelisation with no risk of a burnt patch from an inattentive stove, and lets you walk away for the whole four hours rather than standing over a pot.
2. Build a second, concentrated onion essence by freeze concentration, after the logic Yannick Alléno applies to sauce reductions. Juice a portion of raw onion, freeze it solid, then let it thaw slowly over a sieve: the water melts out first, leaving a small volume of intensely concentrated, unheated onion flavour behind. Stir this into the finished soup off the heat, for a top note the cooked onions alone cannot supply.
3. Finish under a hotter, more controlled grill. A kitchen blowtorch, worked in slow passes, blisters and colours the cheese without the risk of a domestic grill overcooking the toast underneath before the cheese browns.