Prep the tuna. Sprinkle rock salt and leave for an hour. Be generous with the salt.
Rinse off the salt lightly, and pat dry with paper towels.
Put a little olive oil in the pan first, then put in the tuna. Add enough oil to cover the tuna, then put in the ★ ingredients.
Simmer over very low heat for an hour while skimming off the scum. The tuna will be cooked through in 30 minutes, but it will become tender in another 30 minutes.
The oil will change color slightly. After an hour, turn off the heat and leave at room temperature overnight.
Pack into jars that have been sterilized with boiling water. You can freeze this too, but since the tuna is immersed in oil and is not in contact with the air, it will keep for quite a long time in the refrigerator.
The oil as well as the tuna are delicious. Use the oil for stir-fry.
The oil will harden in the refrigerator, but will become liquid again at room temperature. The oil is used for stir-fry and other recipes, and is not wasted at all. It's great spread on bread, too.
Story Behind this Recipe
I researched how to make this, then adapted an authentic recipe a little bit.
Use the tuna in salads, pasta, serve as-is as a drinking appetizer, or put into potato salad. My children love it in yakisoba noodles. You don't need to use a very good cut of tuna. If you tell the fishmonger it can be any shape at all, he will sell you a cheap piece.