Heat chicken stock in a saucepan. In a separate, thick bottomed pan add 3/4 of the butter and the onion. Fry gently for a minute then add the lardons and chicken. Cook for 5 minutes.
Add the rice and stir well to coat each grain of rice, about 3 minutes. The rice should start to become translucent. Very slowly begin to add the stock and vermouth (alternating), a ladle at a time, allowing each to become absorbed by the rice before adding the next.
Continue until the rice is al dente, about 20 minutes. Stir in the remaining butter and half the cheese. Add a small pinch of nutmeg and the remaining cheese sprinkled on top. Serve immediately.