I've made black bean tempeh a few times. I bought a starter pack online. I cooked the beans in an instant pot and waited for them to cool to room temperature. I mixed in the powder (fungal spores, essentially) and let it warm in the instant pot for 24-48 hours. There will be a white mold in and around the bean mixture. The mold should be enough to bind the beans into a loaf.

No one else in my family ate it, so I gave up after two batches. I want to restart using banana leaves as a wrapper, the way they make it in Java. I've also wanted to try out natto, another way of fermenting beans.

Instant pot sounds like a good idea! My housemate built a custom incubator in a styrofoam cooler. We made some good tempeh. We had one batch of good natto, then it went south. When natto goes wrong, it goes REALLY wrong. It's already pretty borderline :P