1Cook the pasta in a large pot of boiling salted water to al dente according to package directions. Drain and return to the pot.
2Preheat the oven to 375°F. Grease a 1 1/2-quart baking dish generously with butter.
3In a frying pan, melt the butter. Saute the mushrooms, thyme, and a pinch of salt, stirring, until the mushrooms are tender. Remove the thyme stems.
4Add the mushrooms, soup, and 1 cup cheese to the cooked pasta. Stir to combine and transfer to the prepared baking dish. Sprinkle evenly with the remaining cheese. Bake until bubbly and golden, about 30 minutes.