Serious French Onion Soup

Put water and the chicken wing tips into a pot without any prep, add 2 pinches of salt, and turn on the heat. Wing tips are rich in gelatin, and having both bone and meat yields a better stock.

Remove the core from the onions, peel them without shaving off the flesh, and trim the ends. Add the peeled skins, cores, and end trimmings to the bouillon pot for stock.

When scum rises, don't skim the first batch right away — push it together with a spatula so it clumps, then remove it all at once. Stir the pot once to float what has settled on the bottom, and skim again. From then on, keep the heat at a gentle, quiet simmer and don't remove too much fat.

Slice 2/3 of the onions along the grain and 1/3 against the grain. Mixing the cuts gives you both pieces that hold their shape and pieces that melt away.

Put butter in a pot and melt it carefully without browning. Once melted, raise the heat and add the onions cut along the grain first, then the ones cut against the grain. Salt and toss to coat, and once the butter has coated all the onions, lower to medium heat and cover.

Steam them under the lid, watching the steam that escapes. When moisture comes out, open the lid and stir once, return the moisture collected on the lid to the pot, and use it to scrape up the browned bits from the bottom. Repeat this every 5 minutes over medium-low heat.

Finely chop the onion, salt it, and let it settle so it releases moisture (do not rinse it in water). Cut the mitsuba into short lengths, then chop it finely.

In a bowl, combine the mitsuba, onion, and whole grain mustard, add lemon juice for acidity, then add olive oil and pepper to make the sauce.

Once the onions' fibers start breaking down, scrape up the Maillard browning again and put the lid back on, cooking them to the absolute limit to concentrate them rather than aiming for color. Don't blast them over high heat — keep steaming them under the lid.

Simmer the bouillon for about an hour, and when the bones slip out easily as you lift the wing tips with tongs, take them out. Shred the meat before it cools and toss it with the sauce made earlier to make the marinated wing tips. Drizzle a little oil to finish.

For the onions, finally take off the lid and raise the heat to drive off the moisture all at once. When the butter and onions start sliding with a sizzle, strain the bouillon into the pot. It thickens from the onions themselves without any added thickener.

Slice the bread and toast it lightly, pour the soup into a bowl, place the bread on top, and cover generously with Gruyère cheese. Bake at 220°C for about 3 minutes, taking it out when the cheese has just melted a little, then finish with a grind of pepper.