1. Peel, cube and salt the sweet potatoes. Peel and finely dice the onions and garlic. Heat 3 tablespoons oil in a wok or pot. Sauté the sweet potato cubes for 3-4 minutes, stirring occasionally.
2. Add to the garlic and onions to the sweet potatoes and stir. Stir in the risotto rice. Pour the white wine in and simmer for two minutes. Gradually add the hot vegetable broth, and keep bringing the rice back to a simmer as you stir it – this will take around 25 minutes.
3. Break the walnuts into coarse pieces and roast them in 1 tablespoon oil in a pan until golden brown. Put the walnuts on a plate with a paper towel on it; wipe the pan clean. Heat remaining oil in a pan. Briefly sauté a few sage leaves in the hot oil, remove with a slotted spoon and blot on paper towels.
4. Grate the parmesan and stir into the risotto; season with salt and pepper. Sprinkle toasted walnuts and sage on top and serve.
Time needed: approx. 45 minutes