French Onion Soup with Gruyère Croutons

Ingredients

• 1.2 litres good beef stock
• 1 tbsp plain flour
• salt and black pepper
• 1.5 kg white onions, peeled and thinly sliced
• 2 sprigs fresh thyme
• 200 ml dry white wine
• 60 g unsalted butter
• 1 tbsp olive oil
• 2 bay leaves
• 1 tsp Worcestershire sauce
• 8 slices baguette, 2cm thick
• 180 g Gruyère cheese, coarsely grated
• Crusty sourdough bread, to serve
• Natural yoghurt, to serve

Method

1. Melt the butter and olive oil together in a large heavy-based pan over medium-low heat. Add the onions and leek with a big pinch of salt — the salt pulls the water out and gets the caramelisation moving. Stir to coat.
2. Cook gently, stirring every 5 minutes, for 50–60 minutes. You're after deep mahogany, jammy, sweet — not pale and softened. Don't be tempted to crank the heat: scorched onions taste bitter, slow onions taste of honey. If the base starts to catch too dark, splash in a tablespoon of water and scrape.
3. Turn the heat up to medium and stir in the flour. Cook for 2 minutes to lose the raw-flour taste. Pour in the white wine, let it bubble hard for 3 minutes, and scrape up every brown stuck bit from the base — that fond is half your flavour.
4. Add the beef stock, red lentils, thyme and bay leaves. Bring to a gentle simmer and cook for 25 minutes, until the lentils have collapsed completely into the broth and the soup has a glossy, full-bodied weight to it. Stir in the Worcestershire sauce.
5. Taste, season, taste again. Adjust the salt and pepper now — at the end, not at the table. The broth should taste rounded and deeply savoury; if it reads flat, it needs salt, not more time.
6. Meanwhile, toast the baguette slices under a hot grill until golden on both sides. Fish out the thyme stalks and bay leaves from the soup.
7. Preheat the grill to high. Ladle the hot soup into 4 ovenproof bowls, float 2 toasted baguette slices on top of each, and pile the Gruyère on generously — right to the edges, so it seals the bowl and crisps against the rim.
8. Sit the bowls on a baking tray and grill for 3–4 minutes until the cheese is melted, bubbling and spotting dark gold. Pull them out, drizzle each with extra virgin olive oil, crack black pepper over the top, and serve immediately — warn anyone at the table that the bowls are screaming hot.