How to Make It
Preheat the oven to 375º and butter an 8-inch-square pan. In a large pot of salted boiling water, cook the pasta until al dente; drain.
Meanwhile, in a saucepan, melt the 2 tablespoons of butter. Whisk in the flour and cook over moderate heat for 1 minute. Gradually whisk in the warmed milk and cook, whisking, until thickened, about 4 minutes. Remove from the heat; stir in the nutmeg, cheddar and cream cheese until melted. Stir in the spinach and cooked pasta; season with the salt.
In a small bowl, mix the rice cereal with the Parmigiano. Transfer the pasta to the prepared pan and sprinkle with the cereal. Bake the mac and cheese for about 20 minutes, until bubbly and golden on top. Serve hot.