Prepare the pasta according to the directions on the back of the box. In a small saute pan, add the mushrooms and ½ tablespoon of butter, sautee until the mushrooms are tender. Set aside.
In a large saucepan, melt the rest of the butter until melted over medium-heat. Whisk in the heavy whipping cream and bring to a boil, whisk in the parmesan cheese, salt, and pepper. Simmer over medium-heat until the mixture has thickened.
Mix in the pasta with the sauce, add in the mushrooms; mix everything together. Pour everything into a 9x13 casserole dish, sprinkle the cheese on top and broil in the oven on high until the cheese has melted.