This is a rarely cooked but classic dish that takes me back to my French training. This version owes more to Heston Blumenthal than tradition, though, with my own spin. It takes time, but not too much effort.
80ml extra virgin olive oil
4 large Spanish onions, cut in 1 cm slices
4 large brown onions, cut in 1 cm slices
6 cloves garlic, finely sliced
1 celery heart, finely sliced
2 star anise
Freshly ground black pepper
7 sprigs thyme
200ml dry white wine
1 1/2 litres quality beef stock (many commercial stocks are sweetened and will not work for this recipe)
50ml dry sherry or dry madeira
1 sourdough batard or baguette, sliced
3 spring onions, finely sliced
200g gruyere cheese, grated
1. Preheat the oven to 130C fan-forced or 150C conventional.
2. In a large ovenproof pot (with a lid that seals), add the oil, onions, garlic, celery and star anise. Sweat over a medium-high heat until lightly caramelised - it will finish cooking in the oven. Season lightly and add the butter, thyme and 80 millilitres of water and stir. Cover the pot and place in the oven for 4½ hours.
3. Remove from the oven and place on a medium-high heat. Remove the star anise and cook to evaporate the juices, stirring continuously.
4. Deglaze with the wine and reduce completely again to a syrup. Add the stock and simmer for 10 minutes - you might not need all of the stock; it shouldn't be a thin soup. Add the sherry, season with salt and plenty of pepper and simmer again for a couple of minutes.
5. To serve, toast bread slices, smear with Dijon mustard, sprinkle with spring onion and gruyere. Serve the soup into bowls and place the toasts on top. Place the bowls under the griller to melt the cheese. Serve immediately.