Step 1 Heat the oven to 275 degrees. Mix together the garlic, ginger, sake, brown sugar and soy sauce in a large, nonreactive, oven-proof pot or casserole. Add the pork and just enough water to cover the pork completely. Cover the pot with 2 layers of foil (and the casserole lid, if using) and cook for 2 to 3 hours, until the pork is fork-tender.
Step 2 Remove the pork from the braising liquid and place in a nonreactive dish. Cover with plastic wrap and refrigerate overnight.
Step 3Cut the pork belly into lardons (1 inch-by- 1/2 inch-by- 1/2 inch). Place them in a large, heavy-bottom saute pan and cook over medium-high heat, stirring frequently until their edges slightly crisp and the fat is mostly rendered, about 10 minutes. Strain and discard the fat. Set aside the meat; you will have about 4 cups, more than is needed for the sandwiches in the final recipe. If not using immediately, cover and refrigerate; reheat before using. The meat will keep for 5 days refrigerated.