Step 1In a large, nonreactive baking dish, place the diced pork fat back, shoulder and belly in separate mounds and sprinkle each evenly with the salt, a pinch of pepper, the bay leaf and thyme. Massage the seasoning into each separate mound with your hands, then cover and refrigerate for 3 days.
Step 2In a medium nonreactive pot, add half the seasoned pork fat and cook over low heat until the fat is melted. Add the remaining pork and cook, stirring often, until the meat is tender, about 1 1/2 hours. Add the onion and shallots and continue to cook until translucent, about 15 minutes. Add the wine and increase the heat so the mixture just simmers. Cook until the wine has evaporated and the meat shreds easily, 20 to 30 minutes.
Step 3Strain the fat from the pork and set both aside until cool enough to handle. Shred the meat with your fingers into a large mixing bowl. Season additionally, if desired. Stir, adding additional fat as needed, until the meat achieves a spreadable consistency.
Step 4Pack the pork in a terrine or nonreactive loaf pan. Lightly cover it with plastic wrap. Place a board or book that will fit inside the pan and weight this down with something heavy, such as a couple of cans or a brick. Refrigerate overnight or longer (Goin recommends 3 days) before serving. Serve at room temperature with coarsely ground black pepper.