cook pasta according to package directions.

preheat oven to 375

melt butter in a lg. saucepan over med. heat. Add flour and cook, stirring constantly, about 1 min. then stir in milk and bring to a boil. Keep stirring and when sauce is well mixed, reduce heat to simmer. Add nutmeg, salt, and pepper.

remove pan from heat and stir in ricotta cheese. Add pasta and toss well, then stir in Swiss cheese and half the cheddar.

Scatter cauliflower in an ovenproof dish and spoon pasta and cheese sauce on top. Smooth top with a spatula and sprinkle on remaining cheddar. Bake 20-30 min. until cheese is nicely browned.