Cut tofu into 2 cm cubes and place in a pan of very hot, salted water while you prepare the rest of the ingredients (do not let the water boil or the tofu will become tough and porous).

Finely slice the green parts of the baby leeks or spring onions at a steep angle.

Heat wok, add oil and reduce heat to medium. Add chilli paste and fry until oil is a rich red color and smells fragrant. Then add black beans and ground chillies (if using). Stir fry for a few seconds then add garlic and ginger. Take care not to overcook seasonings, reduce heat if necessary and let seasonings sizzle until the sauce is rich and fragrant.

Remove the tofu from water with a perforated spoon, shake out excess water and add gently to the sauce, pushing the tofu gently through the sauce and taking care not to break up the tofu.

Add stock or water, white pepper and salt and mix gently, bring to a gentle boil and let simmer for a few minutes until tofu has absorbed the flavours of the sauce.

Add the leek slices now (if you are using them) and simmer until they are tender, then gradually add as much of the cornflour mixture as needed until the sauce thickens and clings nicely to the tofu. If you are using spring onion greens, add these now and stir them gently through the tofu and sauce.

Pour tofu into a bowl, sprinkle with Sichuan pepper and serve with rice and greens.