To make the mushroom dashi: Place the kombu and dried mushrooms in a saucepan with the water and set over a low heat. Slowly bring the water to a very low simmer – you should just see a few little bubbles breaking the surface. Remove from the heat, then leave to infuse for at least 1 hour – it will take a while for the shiitake to fully hydrate and release their flavour into the dashi. Remove the mushrooms and squeeze them out like a sponge, then pass through a sieve and store in the refrigerator for up to one week. The mushrooms will keep in the refrigerator for about four days.
Put the tofu into a small bowl and pour the sake over the tofu. Mix together the cornflour and sesame seeds, then carefully dredge the tofu in the cornflour mixture, ensuring it is evenly coated. Heat the two tablespoons of oil in a non-stick frying pan (skillet) over a medium-high heat and cook for a few minutes on each side, until the tofu is golden brown and crisp. Drain on paper towels and set aside.
Purée the 100ml oil, nori and salt together in a food processor until the seaweed is completely pulverised. Leave the oil to settle while you prepare the rest of the dish.
Bring the dashi, soy sauce and mirin to the boil in a saucepan, then add the daikon rounds. Reduce the heat to a high simmer, place a lid on the pan and cook until the daikon is tender, about 10 minutes. Remove the daikon with a slotted spoon and reserve.
If you’re using shimeji mushrooms, boil them in the dashi for a couple of minutes, then remove and reserve (the enoki don’t need cooking). Keep the dashi at a low simmer with a lid on the pan.
Bring a large pan of water to the boil and blanch the cabbage for one minute, then remove with a slotted spoon and reserve. Let the water come back to the boil and cook the ramen until al dente, according to the packet instructions. Drain very well.
Divide the ramen among four deep bowls, pour over the mushroom dashi and toss the noodles with chopsticks to ensure they aren’t stuck together. Top with the cabbage, daikon, mushrooms, tofu, spring onions, chilli shreds and lemon or yuzu zest.
Finally, add a generous spoonful or two of the nori oil to the surface of the broth. Enjoy immediately.