Blanche the broccoli for 2-3 minutes in boiling water, drain, and set aside. Heat the butter, oil, and flour together, whisking until bubbling, for about 2-3 minutes. Slowly whisk in the milk a little at a time until it is all incorporated and the sauce is bubbling and thickened. Stir in the cheese until melted and then season with salt and pepper to taste.
Combine the broccoli and cheese sauce and pour into a 13x9x2-inch casserole dish. Top with the breadcrumbs and then with the cheese. Bake covered, for 30 minutes, then uncover and place under the broiler for a couple of minutes to brown the top.
Recipe by Cooking With MicheleĀ® at https://cookingwithmichele.com/2015/05/broccoli-casserole-with-fontina-cheese-sauce/