Make the stew
In a pot, heat the duck fat. Add the ham hock and cook over moderate heat, turning, until browned, 5 minutes. Add the chopped onion and carrots, sliced turnip, shredded cabbage, mushrooms and garlic and cook, stirring, until lightly golden, 5 minutes. Add the wine and cook until absorbed. Stir in the thyme, bay leaves, peppercorns and stock; simmer until reduced to 4 cups, 1 hour. Strain into a bowl and wipe out the pot. Return the broth to the pot and bring to a low simmer. Add the baby turnips and carrots and pearl onions, cover and simmer until almost tender, 15 minutes. Add the cabbage pieces and Romanesco, cover and cook until tender, 10 minutes. Stir in the beans and vinegar and season with salt; keep warm.