Cook Pasta according to package directions.
In a large pan over medium heat, add 6 tablespoons of butter; add the mushrooms and ¼ teaspoon salt. Sauté, stirring frequently, until they are cooked through, 3 to 5 minutes.
In a large mixing bowl, combine the mushrooms, cream, cheeses, sage, and remaining salt. Add pasta to the ingredients and toss to combine
Divide the pasta mixture among 6 to 8 individual, shallow, ceramic gratin dishes.
Dot with the remaining 2 tablespoons of butter and bake until bubbly and brown on top, about 7 to 10 minutes.