Preheat the oven to 180°C/360°F/gas mark 4.
Halve or quarter the fresh mushrooms. Heat the oil in a large saucepan, add the mushrooms and cook over a medium heat for 8-10 minutes until they are browned and tender. Pour the stock into the pan, add the grated ginger and dried mushrooms, and bring slowly to the boil. Reduce the heat to a very gentle simmer and leave to cook for about 30 minutes for the mushrooms to infuse the stock.
Meanwhile, toast the walnuts, pumpkin seeds and sesame seeds on a small baking tray in the preheated oven for 4-5 minutes until the walnuts and pumpkin seeds are crisp and the sesame seeds are golden. Leave to cool for 10 minutes and then tip into a food processor. Finely chop the nuts and seeds using the pulse setting, and then add the miso paste, 1 tbsp of soy sauce, the mirin and sugar, and pulse again until combined.
Place the purple sprouting broccoli onto the baking tray, toss with the sesame and sunflower oils, season with sea salt flakes and roast for about 7-10 minutes until the stalks are tender and the tips of the broccoli are crisp.
Meanwhile, add 2 tbsp of the miso paste mixture, the sliced spring onions, the remaining tbsp of soy sauce and the rice wine vinegar to the broth, and simmer for 5 minutes. At the same time, cook the noodles in boiling water following the pack instructions.
Drain the noodles and divide between two deep bowls. Ladle the broth on top and arrange the roasted purple sprouting broccoli on top. Scatter with extra toasted seeds, season with a little shichimi togarashi and serve with extra soy sauce if needed.