Cover the split peas with water and soak overnight so they cook evenly and faster. Split fava beans work too.

Cook on the stove or in a rice cooker until tender enough to bite through while holding their shape. Avoid pressure cookers, which tend to overcook into mush.

Drain thoroughly, return to the warm pot, and stir in 1 tsp vinegar. The acid discourages unwanted bacteria and moulds while helping Rhizopus oligosporus thrive.

Let residual heat dry the surface while stirring occasionally. The peas should feel moist inside but dry on the outside with no visible droplets. Slightly too dry is easier to recover from than too wet.

Cool to about body temperature, then sprinkle the starter evenly and mix thoroughly so every pea meets the spores. Uneven mixing causes patchy growth.

Pack into a perforated tray or bag in a layer 1-1.5 inches thick. Incubate at 86-88F (30-31C) using a dehydrator, oven light, or yogurt setting. White mycelium appears in ~24h; the firm, mushroomy cake is ready in 24-48h.