30 MIN PREP
For the stock
First, Heat your oven to 150C.
Season your oxtail generously with salt. Working in batches, caramelize the oxtail in a large heavy saucepan on medium heat until very well coloured. When all the oxtail is browned, place all pieces back into your saucepan and cover with water. Add the half head of garlic, peppercorns and bay leaves. Return the pot to the heat, and bring to a gentle simmer. Cover with baking paper and a tight-fitting lid, and transfer to the oven.
Braise the oxtail in a slow oven until tender, for 4-5 hours.
When the oxtail is tender, remove the pieces from your stock and place aside. Pass the stock through a fine cloth and discard any residue. Place your stock to the side while you continue with the soup. Once the oxtail is cool enough to handle, shred the meat from the bones. Discard the bones along with any fat and sinew. Set the oxtail aside in the fridge until ready to use.
For the soup
Bring a large pot to medium heat then add 1tbsp of oil and butter. Once butter is foaming, add onions, stir well and season with salt. Stir onions over medium heat until onions are soft with no colour. Reduce your heat to low, and cook gently until golden brown (this should take 1-2 hours). When the onions are suitably caramelised add the brandy and reduce. Then add the bay leaf, fish sauce, cider vinegar, your shredded oxtail and both stocks. Bring to a simmer, reduce heat and cook the soup for a further 20 minutes. Your soup should be thick and rich but you may need to add additional seasonings. Adjust with salt and add a generous few pinches of coarsely black pepper.
Put your oven grill on medium. Slice sourdough bread to a medium thickness, and grill on both sides. Using a ladle, divide the soup evenly into four oven-proof bowls. Top each with a piece of toasted sourdough and a handful of shredded comté. Transfer the bowls to your oven trays, then place underneath the grill. Cook for around 3 minutes, until the cheese is melted, and starting to brown in spots. Serve immediately.