This is the most sure-fire method that I have tried. I have gotten smooth, custard-like tofu with this recipe every time.
'soybeans' on Serious Eats
For some eaters, natto belongs in the nasty bits category of vegetarian fare. Both beloved and reviled, the fermented soybeans are a staple in traditional Japanese cuisine. To make natto, soybeans are cooked for many hours, then inoculated with bacteria and left to ferment in a temperature-controlled fermentation room. But the smell of natto—like a cross between ammonia and rank Camembert cheese—can be off-putting to those without a love for funky tastes and smells.
[Photograph: Chichi Wang] Loosely adapted from Practical Japanese Cooking by Shizuo Tsuji and Koichiro Hata....
These little soybeans can be soaked overnight, then stewed in dashi, sugar, mirin, and soy sauce. Tiny squares of kelp are simmered alongside the soybeans for an extra boost of umami flavor. It's a simple but utterly delicious dish.