Ingredients
For the soup
- 1.2 kg brown onions, peeled and thinly sliced
- 60 ml olive oil
- 30 g butter
- 2 tsp salt
- 4 g sugar
- 1 L beef stock (or vegetable stock)
- 250 ml dry white wine
- 2 sprigs fresh thyme
- 1 bay leaf
- Freshly cracked black pepper to taste
For the toasts
- 1 sourdough baguette, cut into 8 slices (roughly 1.5 cm thick)
- 30 ml olive oil
- 200 g gruyère cheese, thinly sliced or grated
- 15 g finely chopped fresh parsley (optional)
Method
Caramelise the onions
Heat the olive oil and butter in a large heavy-bottomed pot over medium heat until the butter melts and foams, about 2 minutes.
Add all the sliced onions, salt, and sugar. Stir well to coat evenly.
Reduce heat to medium-low and cook, stirring every 5–8 minutes, for 45–50 minutes until the onions are deep golden brown and very soft. This slow cooking develops the rich, complex sweetness essential to the dish.
When ready, the onions should be jam-like in texture and a deep mahogany colour, with no liquid visible when you push them aside.
Build the soup
Pour in the white wine and scrape the bottom of the pot with a wooden spoon to lift all the caramelised bits (the fond). Simmer for 3–4 minutes until reduced by half.
Add the beef stock, thyme sprigs, and bay leaf. Bring to a gentle simmer, then reduce heat to low and simmer for 15 minutes. Season with salt and pepper to taste.
Remove the thyme and bay leaf just before serving.
Make the sourdough toasts
While the soup simmers, preheat your oven to 200°C fan-forced.
Arrange sourdough slices on a baking tray. Brush both sides lightly with olive oil.
Bake for 5–6 minutes until golden and crisp, turning halfway through. Remove and set aside.
Assemble and serve
Preheat your grill to high, or have the oven still at 200°C.
Ladle the hot soup into 4 oven-safe soup bowls, filling each about three-quarters full.
Place 2 toasted sourdough slices on top of each bowl of soup, then divide the gruyère evenly among them, layering it over the bread.
Place the bowls on a baking tray and grill (or bake) for 2–3 minutes until the cheese is melted, bubbling, and lightly golden at the edges.
Carefully remove from the oven (the bowls will be very hot), sprinkle with parsley if desired, and serve immediately.
