Pour in about 3 ladles of the vegetable stock and simmer while stirring. Then gradually pour in the rest of the broth and let the rice swell over low heat. It is ready when it has a slightly soupy consistency, but still has a firm core. This takes about 20-25 minutes.
Dissolve the saffron threads in a little warm water and stir into the risotto. Finally stir in the remaining butter and parmesan. Season to taste with salt and pepper. Serve hot.