In Muroran City, Hokkaido, "yakitori" (literally means grilled chicken) is pork + onion + mustard. The sweet-salty sauce, the umami of the pork and the sweetness of the onion are an addictive flavor combination from my home town!
Put the sauce ingredients in a small pan and heat. Simmer until the sauce is thickened. Keep the sauce into a shallow container or plate.
Cut up a block of pork belly into chunks that can be skewered easily. Cut the onion into wedges.
Put alternate pieces of pork belly and onion on bamboo skewers (in other words, make pork belly skewers).
Grill the skewers on both sides. When the surface of the meat changes color, remove from heat, coat with the sauce from step 2, and grill on both sides again.
Repeat this process of coating with sauce and grilling about 3 times. The sauce will gradually become shiny and will start to smell fragrant.
When the pork and onion have cooked, cool on a plate, and remove from the skewer (it's hard to eat with it on).
Marinade the boiled egg in the leftover sauce (about 10 minutes).
Pack the "yakitori" (actually skewered pork) and the boiled egg cut in half in a bento box. Add Japanese mustard and it's done!
Story Behind this Recipe
"Muroran yakitori" is a local specialty. People from other regions say "it's pork skewers!" but for Muroran locals, pork skewers are "yakitori"! Muroran yakitori goes well with rice! They're well flavored and taste great when cooled! Make a big batch and enjoy with beer too.
If you think there's no need skew the pork and onions, you can grill over a sheet of aluminum foil. You could also cook on a pan, but it's much tastier and fragrant if you grill it! Carefully grilled meat is really yummy!!