In a small bowl, add the miso paste and the warm water. Mix well until the miso dissolves. Set aside.

Finley slice the spring onions and cut the nori, if using, into thin ribbons. Pull the mushrooms apart into bite-sized pieces. Mince the garlic.

Add a few tablespoons of olive oil into a large frying pan, over medium heat. Add the mushrooms and garlic with a sprinkle of salt and pepper. Cook, stirring often, for about 10-15 mins, or until the mushrooms have caramelised.

When the mushrooms are done, remove them from the pan and set aside. Add in the butter and let it melt, then sift over the flour and mix well for about 1 min, until it starts to thicken.

Now, add the soy milk and nutritional yeast. Use a rubber whisk and stir until you have no lumps. Add the miso broth and whisk again. Bring to a gentle simmer for a few mins to thicken slightly.

Meanwhile, cook the tagliatelle as per the package instructions, until al dente. Drain and save a cup of pasta water.

Add the cooked pasta and mushrooms back into the pan. Gently fold and mix to evenly coat the pasta with the sauce and to warm the mushrooms up again. Add a little pasta water to thin down the sauce if needed. Taste and season well with salt and plenty of pepper.

To serve, ladle the pasta into two pasta bowls, top with spring onions, nori and sesame seeds if using.