Gather all the ingredients. Start cooking the rice. Please note that 1½ cups (300 g, 2 rice cooker cups) of uncooked Japanese short-grain rice yield 4⅓ cups (660 g) of cooked white rice, enough for 4 servings. See how to cook short-grain rice with a rice cooker, pot over the stove, Instant Pot, or donabe.
Finely chop ½ onion, 1 rib celery, 1 carrot, and parsley. Set aside the parsley for garnish. Slice 6 mushrooms.
In a large skillet, heat 2 Tbsp extra virgin olive oil on medium high and cook 1 bay leaf until fragrant. Then sauté the onion and the celery until soft.
Add the mushroom and carrot and cook until soft.
Add 12 oz ground beef and pork combination and 4 Tbsp red wine. Use a wooden spoon to break up the meat.
When the meat is almost cooked, add 1 can diced tomatoes with their juice and ½ tsp sugar. Then, add 3–4 cups vegetable stock/broth just enough until all the ingredients are covered. (Don‘t put too much; you will need to reduce the cooking liquid until it‘s almost evaporated).
Add 3 Tbsp ketchup and 3 Tbsp tonkatsu sauce and bring it to a boil.
Skim to remove the excess fat from the soup.
Reduce the heat to medium low and simmer (without a lid) until most of the liquid is evaporated. When you move the meat sauce and see the bottom of the skillet, it’s done cooking. This takes about 2-3 hours, plan accordingly.
Add 1 Tbsp unsalted butter and season with Diamond Crystal kosher salt and freshly ground black pepper.
Butter the baking dish(es) and add 4 servings cooked Japanese short-grain rice.
Pour the meat sauce on top of the rice. Then, sprinkle ¾–1 cup Mozzarella cheese, ¾–1 cup Parmigiano-Reggiano or Parmesan cheese, and 2–3 Tbsp panko (Japanese breadcrumbs) on top.
Preheat oven to 375 and bake for 20 minutes.
Set the oven setting to broil on High. Broil for 2–3 minutes until the cheese is nicely melted and turns a golden color. Garnish with parsley and serve.
You can keep the leftovers in an airtight container and store in the refrigerator for up to 3 days or in the freezer for a month.