Heat the olive oil in a large pot or Dutch oven over medium heat. Add the leek, pumpkin, and celeriac and cook until softened, about 5-7 minutes.
Add the garlic, thyme, and dried mushrooms and cook for another minute until fragrant.
Add the rice (or pasta), tinned tomatoes, cannellini beans, and vegetable stock. Bring to a boil, then reduce heat and simmer for 30-40 minutes, or until the rice/pasta is cooked and the flavors have melded.
Stir in the shredded savoy cabbage during the last 5-10 minutes of cooking.
Season with salt and pepper to taste.
Serve hot, drizzled with a little extra olive oil and grated cheese (optional).