Thick and creamy sauce with a touch of heat and brimming with smokiness from the salmon and freshness from the spinach and tomatoes.
I usually make this using a double batch of Recipe #216441 instead of dry fettuccine.
Bring a large pot of lightly salted water to a boil.
Add pasta and cook for 10 to 15 min or until al dente; drain.
Meanwhile melt the butter in a large skillet and add onion, garlic, and red pepper flakes. Cook over medium heat until onions are translucent. Reduce heat to low and add in milks, cheeses, and basil and stir over low heat until smooth and creamy about 10 to 15 minutes. Add smoked salmon and spinach and toss until heated through. Add cooked pasta and tomatoes and toss to combine. Add a bit of starchy pasta water if needed to make the sauce a good consistency. Season with salt and pepper to taste.