Add the tofu (no need to drain it) and roughly mix it up. Just mix enough to get rid of any big lumps, but there's no need to make it smooth.
Mix the natto with the sauce packet that comes with it. (Use hikiwari (split) natto, or medium sized bean natto, or whatever you like! I prefer small beans.)
Put the Step 2 mixture in a gratin dish (an ovenproof dish), and top with the natto.
Add cheese on top. (I cut up some processed cheese, but, of course, you can use shredded pizza cheese instead.)
Bake in a toaster oven or a 180°C oven for 10 to 15 minutes. When the egg has set, or the top has browned lightly, it's done.
It looks like this inside. It's piping hot and light and creamy.
Story Behind this Recipe
I've been making gratin several times lately (Recipe ID: 387880, Recipe ID: 426071). Even when I get home late, they're easy, healthy, delicious and filling too, so I'm quite addicted to them. I wondered if I could make a simple gratin on my own, and looked in the refrigerator and came up with this.
-Silken tofu has a smoother texture, but firm tofu is OK too. -Don't use the mustard packet that comes with the natto. If the natto didn't come with a sauce packet, use soy sauce instead. -If you are using small eggs, use 150 g of tofu. (But it's really up to you and what you prefer...there's no problem if you change the amounts of ingredients to your liking.