Peel the onions, cut them in half and slice them thinly lengthways along the grain. Fry the onions over a low heat in butter for approx. 40–50 minutes.
They must not boil, but should fry slowly and become increasingly brown until they are eventually a deep brown colour and caramelised. Stir the onions regularly during cooking to prevent them from burning.
Sprinkle a little wheat flour over the onions once they are caramelised and toss them until the flour is absorbed. Then pour first the sherry vinegar, then the wine into the pan and let it reduce almost completely.
Next, add the vegetable stock and bring to the boil. Place the spices and herbs in a muslin or tea bag, tie the bag closed with a string or a knot, and place the spice bag into the soup.
Leave the soup to simmer for approx. 25–30 minutes, then remove the bag. Season the soup with salt and pepper and, if desired, a little more sherry vinegar.
Meanwhile, cut the baguette into thick slices and toast them in the oven at
175 degrees for about 12–14 minutes, until they are completely dry and just slightly golden.
Grate the cheese and switch on the oven’s grill. Divide the soup between some ceramic soup bowls that are ovenproof. Place two slices of bread on top of the soup in each bowl and scatter the grated cheese over the top – yes, you need plenty.
Place the bowls under the grill and brown the cheese until it bubbles and begins to brown.
Remove the bowls from the oven, sprinkle with a few fresh thyme leaves if desired, and serve the soup piping hot.
