Melt 3 tablespoons of the butter in a 12-inch skillet. Add the breadcrumbs and stir to coat with the butter. Cook 5-7 minutes, stirring frequently, until the crumbs are golden and smell toasty. Remove from the heat and stir in the thyme, rosemary, sage and black pepper. Set aside. (Breadcrumbs can be made ahead. Store in a covered container at room temperature up to 3 days.).
Melt the remaining 2 tablespoons butter in a saucepan set over medium-high heat. Add the flour and whisk to blend with the butter. Cook 2 minutes, until the flour mixture looks smooth and creamy. Pour in the milk and add ½ teaspoon salt.
Cook over medium-high heat until you see small bubbles forming on the outside of the pan. Keep stirring until the sauce starts to thicken — this happens in just a few minutes so be sure to keep your eye on it. Cook 3-5 minutes, or until the mixture has the texture of a thick smoothie. Stir in the heavy cream and ½ cup Parmesan and remove from the heat.
Bring 5 quarts of water to a boil and add 1 tablespoon salt. Add the pasta, stir and bring back to a boil. Cook exactly 6 minutes. Drain and transfer to a large mixing bowl.
Add half the Fontina cheese to the pasta. Pour the milk mixture over the pasta and stir to coat. Transfer to a 3-quart baking dish. Sprinkle the remaining Fontina and Parmesan cheeses over the pasta and top evenly with the breadcrumbs.
Bake 20-25 minutes, until the crumbs are golden brown and the sauce is bubbling at the edge of the dish. Serve hot.
Breadcrumbs can be made ahead. Store in a covered container at room temperature up to 3 days.
To make your own fresh breadcrumbs, cut 2 or 3 slices of crusty bread into cubes. Pulse in a food processor until they form coarse crumbs.