Blanch the cabbage leaves

• Bring a large pot of salted water to a boil.
• Blanch the napa cabbage leaves until soft and pliable, then transfer to a bowl of cold water.
• Drain well and pat dry; cut out the thick central stems.

Prepare the filling

• Heat the vegetable oil in a frying pan and sauté the garlic and ginger until fragrant.
• Add the carrot and shiitake mushrooms and cook until softened.
• Stir in the crumbled tofu, spring onion, half of the soy sauce, the sesame oil, salt and white pepper; cook briefly, then take off the heat.
• Mix in the cornstarch to bind the filling.

Roll the cabbage rolls

• Lay a cabbage leaf flat and place a spoonful of filling near the stem end.
• Fold in the sides and roll up tightly, then repeat with the remaining leaves and filling.

Steam the rolls

• Arrange the rolls in a steamer basket, seam side down.
• Steam over simmering water until tender and cooked through.

Make the sauce

• In a small saucepan, combine the vegetable stock, remaining soy sauce and sugar.
• Bring to a simmer and thicken lightly with a little cornstarch slurry.
• Season to taste and spoon the sauce over the steamed cabbage rolls before serving.