French Onion Soup with Gruyère Crouton

Ingredients

• 1.2kg (about 6 large) yellow sweet onions, peeled, halved, and very thinly sliced
• 60g (4 tbsp) unsalted butter
• 1 tbsp (15ml) extra virgin olive oil
• 1 tsp fine sea salt
• 1 tsp caster sugar
• 2 tbsp (30ml) dry sherry or dry vermouth
• 100ml (7 tbsp) dry white wine
• 1.2L rich beef stock (or good-quality vegetable stock)
• 1 bay leaf
• 3 sprigs fresh thyme
• ½ tsp freshly cracked black pepper
• 8 thin slices baguette, sliced on the diagonal
• 160g (1½ cups) Gruyère cheese, freshly grated
• 1 tsp Dijon mustard (optional, for spreading on croutons)

Smart Substitutions

• ↔Use vegetable stock with 2 tsp Marmite or soy sauce instead of beef stock to make this fully vegetarian without losing depth
• ↔Swap Gruyère for Comté or Emmental for a slightly different flavour — both melt equally well

How to Cook

1. 1

   Melt butter with olive oil in a large, wide, heavy-bottomed pot (a Dutch oven is ideal) over medium heat. Add all the sliced onions and salt. Stir to coat. Reduce heat to medium-low. Cook, stirring every 5–7 minutes, for a full 45–50 minutes until the onions are deeply caramelized — dark mahogany-brown throughout, dramatically reduced in volume, and incredibly fragrant.

   50 min

   This is not a step where you can speed up by increasing heat. Medium-low heat is mandatory. High heat caramelizes the surface and burns the bottom while the centre remains raw and sharp — you need even, slow heat throughout. Use a wide pot and stir the bottom and corners specifically.

2. 2

   Add sugar in the final 5 minutes of caramelizing if the onions still look pale — it accelerates the Maillard reaction. Add sherry, scraping up all the dark fond (caramelized bits stuck to the bottom) with a wooden spoon. Cook until the alcohol evaporates, then add white wine and reduce by half.

   5 min

   The dark fond on the bottom of the pot is concentrated, caramelized flavour — the deglazing liquid lifts it all back into the soup. This is where a significant portion of the soup's depth comes from.

3. 3

   Add the stock, bay leaf, thyme sprigs, and black pepper. Bring to a gentle simmer. Cook uncovered for 20 minutes to let the flavours meld and the soup reduce slightly. Taste and adjust seasoning — it should be rich, sweet, and deeply savoury.

   20 min

   If the soup tastes one-dimensional after simmering, add 1 tsp soy sauce or a small piece of Parmesan rind — both are natural glutamate boosters that add umami depth without being detectable.

4. 4

   Toast the baguette slices under the grill until golden on both sides. Spread with Dijon mustard if using. Preheat the grill (broiler) to high. Ladle the soup into 4 oven-safe bowls placed on a baking sheet. Float 2 croutons on top of each bowl. Pile Gruyère generously over the croutons. Slide under the grill for 3–4 minutes until the cheese is melted, bubbling, and blistered. Serve immediately.

   8 min

   Overfilling the bowls is intentional — the crouton should sit proud above the bowl rim, and the cheese should drape down the sides of the bowl and caramelize against the ceramic. This is the signature presentation.