Heat oven to 475°. Bring a large pot of salted water to boil.

For the béchamel: In a medium saucepan, heat milk over medium-low heat; bring just to boil then remove from heat. In a large saucepan, melt butter over low heat. Add flour; cook, stirring constantly with a wooden spoon for 2 minutes. Do not brown. Remove from heat. Add 2 tablespoons milk to flour mixture, stirring constantly until milk is incorporated. Repeat until ½ cup of the milk has been added. Add remaining milk ½ cup at a time, incorporating between additions, until all milk has been added. Return to low heat and cook, stirring frequently, especially along corners of pan, until béchamel is the consistency of thick cream. Stir in salt, season with nutmeg and remove from heat; cover to keep warm.

For the pasta: Combine fontina, asiago and gorgonzola in a large bowl. Cook pasta in boiling water until al dente. Drain pasta, immediately add to bowl with cheese, add béchamel and toss together to combine well. Transfer pasta to a baking dish, sprinkle with Parmigiano-Reggiano and bake until heated through, about 10 minutes. Serve immediately.