This doesn't need to be made just with flounder, since this recipe will make any white fish taste delicious.
I wanted to make something with just a small amount of simmering sauce. When I tried simmering the fish in a frying pan, it came out delicious.
Don't simmer the fish over high heat, but keep the it around medium when boiling for 15 minutes. Otherwise, the flesh of the fish will fall apart, so please be careful.
Enjoy Japanese food around the world.