2 tbsp vegetable oil
100g (3.5 oz) unsalted butter
6 large onions (about 1.5kg/3.3 lb), finely sliced
6 cups beef stock
2 star anise
2 bay leaves
1 cup Chinese Shaoxing cooking wine
2 tbsp finely grated ginger
2 tbsp soy sauce
3 tbsp corn flour (cornstarch), mixed with 3 tbsp water
4 slices bread, lightly toasted
2 cups (about 100g/3.5 oz) grated gruyere or cheddar cheese
2 tbsp finely sliced chives
Heat the oil and the butter in a large pot over medium-high heat. When the butter is foaming, add the onions and season with 2 teaspoons of sea salt. Cook, stirring every so often, for about an hour or until the onions are super jammy and deeply golden brown.
In the meantime, place the stock in a saucepan over high heat. Add the star anise and the bay leaves. Bring to a boil, then turn the heat off and allow to infuse while the onions cook.
Preheat oven grill to high.
When the onions are ready, add the Chinese cooking wine. Simmer for 3-4 minutes. Add the ginger. Then strain the stock straight into the pot. Simmer for another 5 minutes. Then add the soy sauce and the corn flour mixture. Simmer for another 2 minutes or until the soup has thickened slightly. Taste and season with salt to taste.
Ladle the warm soup into oven-proof ramekins or soup bowls. Place the toasts on top of the soup. Pile the cheese up on top of the toasts and soup. Place under the hot grill until golden and bubbling. Sprinkle with the chives and serve immediately.