Pre-heat the oven to 180°c / gas mark 5.
Put the sweet potato in a roasting pan and put in the oven until cooked – roughly 10-15 minutes. Once a fork goes in easily it's done. When it's done, set aside for later.
600 g sweet potatoes
While the sweet potato is roasting, soak the noodles in a bowl/pan of freshly boiled water. You shouldn't need to put them on to cook (if you're not using rice noodles, follow your packet instructions). Put to one side.
200 g flat rice noodles
Add all the paste ingredients to a blender and blend until smooth. You can also do this in a pestle and mortar – just omit the water.
2 shallots, 1.5 tablespoon fresh ginger, 1 tablespoon fresh turmeric*, 1.5 tablespoon coriander seeds, 4 cardamom pods, 2 cloves garlic, 1 teaspoon curry powder, 1 teaspoon fermented soybean paste*, 4 tablespoon water
Now get the wok on to a medium-high heat and add a splash of oil.
Add the khao soi paste and fry for around a minute until fragrant. Then add the tofu and coat well in the paste by mixing.
Khao Soi paste, 400 g extra-firm tofu
Pour in the coconut milk and stock. Bring the mix up to a boil, then reduce to a simmer.
400 ml coconut milk, 750 ml vegetable stock
Add the sugar and vegan fish sauce (or soy sauce). Continue to simmer for another 10 minutes.
1 tablespoon sugar, 2 tablespoon vegan fish sauce
Try it and add more sugar or vegan fish sauce (or soy sauce) to taste.
Put the sweet potato and spring greens in for a couple of minutes – just until the greens have wilted and the sweet potato has heated back through.
600 g sweet potatoes, 100 g spring greens
Drain the noodles and split into four portions. Ladle the soup on top. Garnish with crispy fried shallots, plus chilli flakes fried in oil for the spice lovers.