Heat oven to 350F. Bring a 4-quart saucepan of salted water to a
boil. Add the pasta and cook until not quite al dente, about 7 minutes. Drain
pasta, transfer to a bowl, and set aside. Melt 3 tbsp. of the butter in a 4-qt.
saucepan over low heat. Add the bread crumbs and Parmesan, toss to combine, and
transfer to a small bowl; set aside. Wipe out the saucepan and set over medium
heat. Melt the remaining butter and whisk in the flour until smooth. Whisk in
the milk and cook, continuing to whisk often, until the sauce coats the back of
a spoon, about 10 minutes. Stir in the Gruyère, 1 cup of the Comté, and 1 cup of
the Fontina and whisk until the cheese is melted and incorporated. Season with
salt and pepper. Remove pan from heat and stir in the reserved pasta. Pour the
mixture into a 2-quart baking dish and top with the remaining Comté and Fontina.
Sprinkle bread crumb mixture over the top and bake until golden brown and
bubbly, about 30 minutes. Let cool for 10 minutes before serving.