Bring large pot of lightly salted water to boiling. Whisk together half-and-half, milk, flour, nutmeg and red pepper in medium-size bowl.
Cook mushrooms with salt and pepper in saucepan over high heat 15 minutes, until moisture from mushrooms has evaporated. Add wine; cook, stirring, 2 minutes.
Add pasta to boiling water; cook until al dente, tender but still firm. Drain; transfer to bowl.
Meanwhile, add half-and-half mixture to mushrooms in saucepan; cook until mixture starts to thicken and bubble, 5 to 8 minutes. Whisk in cheeses until fairly smooth.
Pour sauce over pasta; stir well to coat. Top with scallion. Serve. Makes 6 servings.