Peel and finely chop the onion and sweat in hot olive oil while stirring. Sprinkle in the rice, sweat until translucent and deglaze with red wine. Bring to the boil and cook the rice, stirring, until the liquid has evaporated. Gradually pour in the vegetable stock in small portions and let it boil over and over again, stirring constantly. As soon as the soup has evaporated, stir in the butter, parmesan, salt and pepper. Serve hot.