To Make the Oxtail

1. Place an 8 quart pressure cooker over medium heat and add enough olive oil to cover the bottom. Add the celeriac, leeks and carrots and cook for about 10 minutes or until softened, stirring frequently. Remove from the pressure cooker and set aside. Add the butter. Cook the onions and star anise in the butter until lightly browned, about 10 minutes. Add the vegetables back in and continue cooking for 5 minutes. The bottom of the pan may turn brown, this is OK.
2. Remove everything and set aside. Pour the water into the pressure cooker and scrape the bottom to get off all the browned bits. Pour the water over the vegetables.
3. Put the pot back on high heat, cover the bottom with olive oil and start adding the meat, working in batches if necessary. Brown the meat on all sides. Remove from the cooker and set aside. Deglaze with the wine and beer. Add the chicken stock, peppercorns, bayleaf, thyme and tomatoes. Stir in the vegetables and oxtail you set aside.
4. Close the lid and cook at a gauge pressure of 1 bar for 2 hours (start timing once the gauge pressure has been reached). Once the oxtail has finished cooking, take the pressure cooker off the heat and allow to cool for 45 minutes. Skipping this step will yield dry meat. Carefully remove it from the pot. Strain the remaining content of the cooker through a fine mesh sieve, reserving the liquid.
5. Pour the liquid into a medium pot and reduce by 2/3, about 45 minutes. Remove 1/2 cup and reduce further to a syrupy/demi-glace consistency. Set aside.
6. Remove the meat from the bones and add to the less reduced sauce.

To Make the Infused Salt

1. Grind the star anise and black pepper in a spice or coffee grinder (or crush into a powder with a pestle and mortar) and gently toss with the fleur de sel flakes. Set aside.

To Make the Pasta

1. Sift the flour together with the semolina on a clean working space. Add the salt and make a well in the middle. Add the eggs and the egg yolk to the well with the water and work into a smooth dough. Vacuum pack (or alternatively wrap in cling foil). Refrigerate for at least 1 hour (or up to overnight – this can be made in advance).
2. When ready to serve, remove the dough from the refrigerator. Roll out with a pasta machine and cut into fettuccine. Allow to dry for 30 minutes before cooking al dente in well salted boiling water.

To Make the Caramelized Onions

1. Toss the sliced onions for caramelizing with the baking soda. Divide evenly among four 8oz canning jars and top with an equal amount of butter each. Firmly close the lids, then open 1/4 turn to make sure the jars don’t explode in the pressure cooker.
2. Add a metal rack to an 8 quart pressure cooker and place the jars on top. Cover the bottom of the cooker with 2.5cm (1in) water. Close the lid and cook at a gauge pressure of 1 bar for 40 minutes. Allow to fully cool before opening the jars to prevent splattering.
3. Add the pressure cooked onions to a medium pan and reduce for about 20 minutes or until the liquid has reached a syrupy consistency. Season with salt.