French onion soup with St Gall croûtes

St Gall is a firm Irish cheese made from unpasteurised cow’s milk. Similar to Emmenthal, St Gall has a yellow centre with small round holes. It has a creamy, velvety texture with a sweet, rich, nutty flavour, likened to peanuts or hazelnuts.

Ingredients (serves 4): 75g butter; 1kg onions, peeled and sliced; Sea salt and freshly ground black pepper; 2 bay leaves; 1 tbsp thyme leaves; 75ml dry sherry; 1 tbsp plain flour; 1½ litres brown beef stock; 150g St Gall cheese, grated; 1 tsp Dijon mustard; 4 thick slices of baguette

Method

Melt the butter in a large heavy-based saucepan and sweat the onions with some salt and pepper, the bay leaves and thyme for 15 minutes. Uncover, then continue to cook the onions gently, stirring from time to time. It should take about 45 minutes for the onions to soften and release their natural sugars, which will caramelise.
Once the onions turn meltingly soft and deep golden, stir in the sherry and simmer rapidly until almost completely reduced. Sprinkle over the flour, give it a stir and cook for 2 minutes. Pour in the beef stock while stirring and bring to the boil. Check for seasoning, then reduce the heat and simmer for another 20-30 minutes.
Preheat the oven to 220C/Gas 7. Divide the soup between heatproof bowls. Mix the St Gall with the mustard and some seasoning and spread on top of the baguette slices. Place them on top of the soup. Put the bowls uncovered in the oven until the soup is bubbling up through the bread and the cheese is golden brown.