Best of the best French onion soup

Method

1. Begin with the stock. Heat the oven to 180°C fan/gas 6 and put the chicken carcass on a tray. Roast for 30 minutes until a rich reddish, dark brown – do keep an eye on it, as if you take it too far and it begins blackening it will taste too bitter and be ruined. While it roasts, slice the onion, leek, carrot and mushroom (saving any peels, roots and trimmings) and heat a dash of oil in a large stock pot over a low-medium heat. Add the sliced veg and cook until caramelised, stirring occasionally – they should be nicely done by the time the bones are ready.
2. Meanwhile, finely slice the onions and shallots for the soup (again, saving the roots and peels for the stock) and add to a large, heavy-based saucepan with a lid. Put in the butter and a large pinch of salt, cover and cook over a low heat for 2 hours, stirring often, then removing the lid after the first hour. They’re ready when deeply sticky and brown – they will begin to catch quite regularly towards the end, so keep your eye on it.
3. Once it’s roasted, add the carcass to the stock pot of veg, then put the oven tray over the heat and deglaze with a splash of the red wine. Scrape off the tasty bits and add it all to the pot too. Add the rest of the red wine, bring to a simmer and reduce by half, then top up with 2 litres cold water. Bring to the boil and skim off the scum/foam that rises to the top. Turn down to a simmer and add all your reserved roots, peels and any veg trimmings (if using), along with the dried mushrooms, bay leaves, thyme and peppercorns. Simmer for 2 hours or until the onions in the other pan are done.
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4. Strain the stock through a fine sieve into a bowl or jug – you want about 1 litre. Stir in 1 tsp Bovril: taste and add more Bovril, salt and black pepper if needed.
5. Now you’ve taken the time to make these two exquisite elements, the soup itself is easy. Add the marsala or sherry to the pan with the onions and bubble for a few minutes until reduced by half. Pour in the stock and gently simmer for 20 minutes – this is just to heat through and amalgamate the flavours – it doesn’t need to reduce. Season with the vinegar, Worcestershire sauce, salt and pepper. Keep warm.
6. To serve, heat the grill to medium-high and toast the baguette slices under it on both sides. Rub one side of each slice with a raw clove of peeled garlic. Divide the soup among 4 ovenproof bowls, then top with the bread, followed by lots of grated comté. Put the bowls back under the grill to melt (if you don’t own 4 ovenproof bowls, you can put the toasts on a baking tray and grill them first, then add them to the soup). Finish the dish with plenty of finely chopped chives and a generous crack of black pepper.