Instructions
Step 1
Make the pot-au-feu: To a large pot, add the beef shanks, shoulder clod roast, carrots, parsnips, turnips, leeks, onions, and cabbage. Using twine, tie the parsley, peppercorns, bay leaf, and garlic in a piece of cheesecloth and add to the pot. Add enough cold water to cover the meat and vegetables (7–9 quarts), season generously with salt, and bring to a boil. Turn the heat to medium and simmer, skimming any foam that rises to the surface, until the meat is nearly cooked, about 1½ hours. Add the potatoes and simmer until the meat flakes easily when pierced with a fork, about 1 hour more. Season to taste with salt and black pepper.
Step 2
Meanwhile, make the sauce gribiche: In a medium bowl, whisk 2 teaspoons of the vinegar, the mustard powder, egg yolk, and 2 teaspoons of water until foamy. Whisking continuously, very gradually add the vegetable oil, starting with a few drops at a time, until all the oil is incorporated and a thick sauce forms. (Alternatively, in a food processor or blender, pulse together 2 teaspoons of the vinegar, the mustard powder, egg yolk, and 2 teaspoons of water. With the motor running, in a slow, steady stream, add the oil and blend until thick.) Stir in the remaining vinegar, the capers, chervil, parsley, and tarragon. Through a fine-mesh strainer, press the hard-boiled egg into the sauce and stir to combine. Season to taste with salt and black pepper. Cover and refrigerate.
Step 3
Make the tomato sauce: Position a rack in the top third of the oven and preheat the broiler. On a baking sheet, place the tomatoes and broil, turning occasionally, until the skins are blackened in spots and the flesh is very soft, 10–12 minutes. Set aside until cool enough to handle, then peel, core, seed, and chop the tomatoes and transfer to a bowl. Stir in the olive oil and hot sauce and season with salt and black pepper to taste.
Step 4
Serve the pot-au-feu: For the first course, using a ladle, strain some of the broth into four soup bowls. For the second course, use a spider skimmer to transfer the vegetables and shanks to one side of a large warmed platter. Transfer the roast to a cutting board, discard the twine, and slice thickly. Place meat and any accumulated juices on the other side of the platter, then ladle some of the remaining broth over the top. (Strain any remaining broth and reserve for another use.) Serve with the gribiche and tomato sauces on the side.