Place the tofu into one bowl and the dried shiitake mushrooms in another. Cover the tofu with freshly boiled water and soak for 10 minutes, then drain well.
Cover the shiitake with 400ml (14fl oz) of hot water and soak them for 5 minutes, then drain them, reserving the soaking liquid. Finely chop the rehydrated shiitake.
Put the sesame seeds in a small heatproof bowl with the chilli flakes and the Sichuan pepper. In a microwave or small saucepan, heat the oil with the slice of ginger until it just begins to bubble, then pour this over the sesame-seed and chilli mixture and stir well. Put to one side.
Heat the sesame oil in a frying pan over a medium heat. Add the white parts of the spring onion, the garlic and the grated ginger and fry for 1 minute, until just soft.
Add the grated fresh mushrooms and finely chopped rehydrated mushrooms and cook for 8–10 minutes, until the water is released and has cooked away and the mixture begins to stick.
Measure out 250ml (9fl oz) of the mushroom soaking liquid and mix the cornflour into it. Add the sugar and soy sauce, then add the mixture to the pan.
Bring the liquid to a boil, and cook for 3 minutes, until it thickens to the consistency of single cream.
Add the tofu and simmer gently for 2 minutes to heat through, then stir through the sesame and chilli oil (along with all the sesame and spices, but remove the slice of ginger), and add salt to taste.
Serve topped with the green parts of the spring onions and with steamed rice on the side.
