Clean the mushrooms and slice them. Add 2 tablespoons of butter to a skillet over medium-low heat. Once melted, add the mushrooms and garlic. Saute the mushrooms for 6-8 minutes. Add the rest of the butter and heavy cream. Let it simmer over low heat.
In the meantime, cook the pasta according to package instructions in a large pot. Drain the pasta and reserve a cup of pasta water. Return the pasta to the pan.
Add the mushroom sauce to the pan with pasta. Mix thoroughly. Add parmesan and a few ounces of the pasta water at a time until it reaches a creamy consistency. Season with salt and pepper. Serve and garnish with parsley.