Philly Cheesesteak Enchiladas

1lb steak, sliced thin 1 medium onion, sliced 7 flour tortillas 8 Tbsps. unsalted butter, divided 2 Tbsps. butter 1 cup milk 1 cup provolone cheese 1 cup Swiss cheese 1 cup mozzarella cheese Preheat oven to 350°F. Lightly spray 9x13” baking dish with cooking spray and set aside. Heat 3 tablespoons butter in large skillet over medium heat. Add onion and heat until tender, about 5-7 minutes. Remove from skillet and set aside. Add steak to skillet and season to taste. Cook 5 minutes or until browned and garlic is fragrant. Drain excess fat. Melt remaining butter in large saucepan over medium heat. Add flour and whisk into melted butter until smooth. Cook and stir on medium heat for 2 minutes. Slowly whisk in milk. Stir in provolone and Swiss cheese. Melt completely. Reduce to simmer and cook 5 minutes. Remove from heat. Sauce will thicken as it cools. Layer tortillas with steak and onions and top with mozzarella cheese. Tightly roll each tortilla and place seam side down in baking sheet. Top with remaining mozzarella cheese. Pour cheese sauce over enchiladas. Bake 20 minutes or until heated through and bubbly. Serve hot.