Wrap the silken tofu in paper towels and put on a sieve. Weight it down and leave to drain for half a day. Finely chop the onion.
Combine the drained tofu, ground meat, egg, katakuriko, onion, nutmeg, salt and pepper, and mix together well until smooth.
Refrigerate the mixture for about an hour.
Form the mixture into patties. It's very soft so do this just before you'll cook them.
Heat a frying pan over medium heat and add the hamburgers. Brown well (so that the juices are trapped inside). Flip over and brown the other side.
When both sides are browned, flip them over again, cover with a lid and turn the heat down to low. Steam-cook the hamburgers (5 to 10 minutes). If the juices run clear when you press down on them, they are done.
Combine the sauce ingredients in a small pan and simmer.
Transfer to serving plates, pour the sauce over it, and serve.
Story Behind this Recipe
I usually make this with firm tofu, but I tried making it with silken tofu and it was delicious!
The onion is not sautéed, so this is very easy to make! If you don't have nutmeg, add a little juice from a grated ginger.