Season the oxtails with salt and pepper and dust each piece with a little flour. Sear the oxtails in a cast iron casserole with a little oil until golden brown. Transfer to a perforated pan or a rack set over a plate to drain the extra fat.
In a braising pan, sweat the mirepoix in a little oil. Add the tomato paste and cook together with the vegetables. Deglaze the pan with the sherry and a little of the red wine, stirring and scraping the pan to release the stuck-on flavor. Add the remaining red wine, bring to a simmer, and let the alcohol evaporate. Add the veal stock and bay leaf. Put the oxtails in the sauce, cover the pan, and braise until the meat falls easily off the bone with a fork, about 2 1/2 hours. When cool enough to handle but still warm, separate the meat from bones. Strain and reserve the braising jus.
To make the bread stuffing:
Heat 1 tablespoon of the oil in a large pan over medium high heat and add the bread cubes, tossing them until they're toasted. Transfer to a large bowl. Pour the milk in a dish and season with salt, pepper, and nutmeg. Pour the milk over the bread and let it get completely absorbed.
Meanwhile, heat the remaining tablespoon of sunflower oil in a skillet over medium heat. Add the onions and cook until they're softened but have not taken on any color. Add them to the bread mixture. Let the mixture cool to body temperature and then add the egg yolks. Add parsley. Mix everything together and put in a pastry bag.
To make the crepinette:
Line the inside of a 5-inch ring mold with caul fat. Place 3 ounces of the braised oxtail meat along the inside of the mold and pipe some bread stuffing in the remaining space inside the mold. Close the crepinette with overlapping caul fat, making sure the crepinette is holding together. Place the crepinette in a pan and cover with some of the reserved braising jus. Cook simmering over medium heat, until fully cooked through.
To make the liquid Yukon gold mash:
Put the potatoes in a saucepan with the stock, water, thyme, rosemary, and bacon. Bring to a boil and cook until the potatoes are tender. Drain the potatoes. Peel them and process through a potato ricer while still hot. Work in the cold butter and hot milk to get a creamy and runny mash.
To make the truffle jus:
Cook the remaining braising jus in a saucepan until reduced by one-third, continually degreasing the upcoming fat. Add the chopped black truffle and truffle jus.
Put a generous spoonful of the liquid Yukon gold mash in the middle of the plate. Place the crepinette on top and drizzle the truffle jus on top.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.