Preheat the oven to 200°C / 400°F. Line the baking tray if desired.

Add the walnuts and mushrooms to the food processor. Pulse until they form a coarse mince.

Spread the mushroom-walnut mince over the baking tray. Toss it with 1 tablespoon olive oil and 1/2 teaspoon salt.

Roast the vegetable mince for 15 min at 200°C / 400°F. Stir it thoroughly.

Roast for another 15 min until browned and dry-looking. Remove the tray from the oven.

Finely chop the onion and celery stalks. Set them aside.

Heat the remaining 2 tablespoons olive oil in the large frying pan over medium heat. Sauté the onion and celery for 5 to 7 min until softened.

Add the tomato paste and optional miso paste to the pan. Cook for 2 min, stirring, until the paste darkens slightly.

Pour the balsamic vinegar into the pan. Scrape the browned bits from the base of the pan.

Add the roasted mushroom-walnut mince and 375 ml water to the pan. Stir until evenly combined.

Season the sauce with the remaining salt, black pepper, paprika, dried Italian herbs, and bay leaves. Bring the sauce to a gentle simmer.

Simmer the ragù for at least 20 min over low heat. Add up to 125 ml more water if the sauce becomes too thick.

Bring a large pot of salted water to a boil. Cook the dried pasta until just under al dente according to the package timing.

Reserve about 120 ml pasta water and drain the pasta. Remove the bay leaves from the ragù.

Add the drained pasta to the ragù. Toss for 1 to 2 min, adding reserved pasta water as needed until the pasta is coated and al dente.