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1
Place the pork belly cubes in a pot with the shimofuri sake, sliced ginger, and enough cold water to cover. Bring to a full boil and cook for 10 minutes. Drain and rinse each cube under cold running water. The surface of the meat should be visibly clean — no grey foam, no blood residue.
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2
Pat the blanched pork dry. Heat neutral oil or rendered pork fat in a heavy casserole over medium heat. Brown the pork cubes on all sides until a deep mahogany crust forms. The pan should sizzle steadily throughout — a dull sizzle indicates insufficient heat for Maillard development.
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3
Pour off excess fat from the casserole. Add the braise sake, mirin, soy sauce, sugar, and water. Bring to a gentle simmer. Set an otoshibuta (drop lid) directly on the surface of the liquid and pork. Reduce heat to the lowest possible setting and braise for a minimum of 2 hours, up to 4. This is where the dish lives or dies: sustained low heat is the sole condition under which collagen converts to gelatin and the fat renders to translucence without the muscle fibres toughening — any rolling boil will seize the meat irreversibly. At 2 hours, press a cube with a finger; it should yield and tremble, offering almost no resistance.
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4
Remove the pork carefully and set aside. Raise the heat under the braising liquid and reduce until it thickens to a glossy, lacquered glaze — it should coat the back of a spoon and fall in slow, heavy drops. Watch closely: the high sugar content will scorch if the pan is left unattended.
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5
Return the pork to the casserole and turn each cube to coat thoroughly in the glaze. Allow the pork to rest briefly in the liquid off the heat — the flavour penetrates further as the temperature equalises. The glaze should adhere as a dark, shining coat. Serve with prepared karashi alongside.