Heat the chicken stock to boiling in a saucepan, then reduce the heat and hold at a simmer.
Heat the butter and oil in a wide heavy saucepan over low heat. Add the onions and cook until translucent, about 5 minutes. Add the rice and cook, stirring to coat with butter, until opaque, about 3 minutes.
Combine the ingredients for gremolata and add to the risotto with the vegetables. Cook, stirring constantly, 2 more minutes. Season with salt and pepper to taste. Sprinkle with the Parmesan and serve at once.