Place a medium saucepan over low heat. Add the chicken stock and heat until warmed through.
Place a large pot over medium heat. Add the olive oil. Once hot, add the rice and stir quickly for 1-2 minutes, or until it has a slightly nutty smell. Add 1/4 cup of wine to the pot and keep stirring the rice until the liquid is almost gone.
Add 1 ladle full of the warm broth to the pot. Continue stirring until the liquid is absorbed. Repeat adding the broth and stirring until it is absorbed, until all of the broth has been incorporated. The rice should have a porridge-like texture.
While the rice is cooking, melt the butter in a large skillet over medium-high heat. Once hot, add the onions and cook for 2-3 minutes until softened, stirring often. Add the mushrooms and cook until they are browned and tender.
Add 1/4 cup of wine to the mushrooms. Cook until the liquid has reduced by half. Add heavy cream and continue to cook until the liquid has reduced by half again.
Stir the Parmesan cheese into the risotto until melted. Check the seasoning and add salt and pepper to taste.
Serve the risotto and spoon the mushroom sauce over each portion, dividing it evenly between the plates.