This soup is all about creating a beautiful dish out of next to nothing; about producing mountains of flavour from the most modest of ingredients: the humble onion. But it also has everything to do with that gratinated cheese crust. It is best served with this column.

Ingredients

5 large onions, halved and then sliced thinly

5 leeks, washed and chopped

3 garlic cloves, finely chopped

4 thyme sprigs, the leaves picked off

1 Tbsp caramel sugar (optional)

6 Tbsp butter

3 Tbsp flour or cornflour

300 ml chicken stock

1 litre beef stock

50 ml Cognac, optional

50 ml sweet Sherry, optional

300 g Mozzarella (unless you can source Gruyère, which is the best choice, or Fontina), grated

Slices of toasted baguette, enough to cover the top of the dish you’ll be using when the cooked soup goes into the oven

150 g Parmesan, grated

Salt and white pepper to taste

Method

Sauté the onions for two hours on a very low heat, stirring occasionally. After the first hour add the leeks, garlic and thyme and continue cooking. Also sprinkle the sugar over now if using, but if it is caramelising beautifully after an hour you might not want to. Return to the pan every few minutes; if you leave it untended for too long the onion is likely to burn and the flavour be ruined.

Melt the butter in a heavy pan large enough to hold all the onions plus the stock. Off the heat, whisk in the flour or cornflour. It should be a slurry more than the kind of roux you’d use for a béchamel, what is known as a “soft roux”. 

Tip the caramelised chopped onions into this roux on a low heat while stirring or whisking. Add the chicken stock and beef stock and stir very well to combine. Season with salt and white pepper to taste.

Pour the soup into an ovenproof crock or casserole. Lightly toast slices of baguette and place them over the top to cover the soup entirely. Grate a generous amount of the cheese you’re using and pile it over the top so that you can’t see any of the baguette beneath.

Put it in a preheated oven at 200℃ for an hour or until the cheeses have melted into the bread and turned golden. Garnish with picked thyme leaves. DM/TGIFood

Tony Jackman is Galliova Food Champion 2021. His book, foodSTUFF, is available in the DM Shop. Buy it here. 

Follow Tony Jackman on Instagram @tony_jackman_cooks. Share your versions of his recipes with him on Instagram and he’ll see them and respond.

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