(6 servings)
Fill a 4 to 5-quart pot about three-fouths full with water and add 1 tablespoon salt. Bring to a boil and add the pasta. Cook, stirring once or twice, until tender but firm, about 10 to 12 minutes, and drain. Set pasta aside and reserve the pot.
In a medium skillet, melt 3 tablespoons of the butter over medium heat. Add the garlic and mushrooms and cook until soft and creamy in texture, 6 to 8 minutes. Add the thyme and a generous amount of salt and pepper to taste. Keep warm.
Using the same pot you used to make the pasta, melt the remaining 2 tablespoons of butter over medium heat. Slowly whisk in the flour and stir constantly until a paste forms, 30 to 45 seconds. Continue stirring for 1 to 2 minutes more, until the mixture starts to darken slightly and smell a bit nutty. Slowly whisk in the milk, cream, and the remaining 1 teaspoon salt and cook until the mixture starts to thicken and is just beginning to bubble around the edges, 5 to 7 minutes. It should be thick enough to coat the
back of a wooden spoon. Add the cheeses and nutmeg, and stir until the cheeses have melted and the sauce is smooth. It should be similar in texture to cake batter. If it’s soupy, continue cooking until it thickens.
Add the pasta and mushrooms and stir until the mushrooms are warmed through and the mixture is combined.
Ladle into bowls and sprinkle with more black pepper and parsley for garnish. Serve right away.