Sauté the mushrooms.
In a large pan over medium heat, melt the butter.
Add the sliced mushrooms and cook until softened and golden, about 5-7 minutes.
Add onion to the pan.
Stir in the chopped onion and cook until translucent.
This should take about 3 minutes.
Pour in the rice.
Add the Arborio rice to the pan, stirring well for about 2 minutes until lightly toasted.
Add wine and stock.
Pour in the white wine and cook until evaporated.
Begin adding the chicken stock one ladle at a time, stirring constantly.
Wait until each addition is absorbed before adding the next.
Finish with cheese.
Once the rice is creamy and al dente, stir in the grated Parmesan.
Season with salt and pepper to taste.
Serve immediately.