Classic Mac ?n Cheese

Preheat the oven to 375? F. Coat an 8x8-inch square baking pan with cooking spray. In heavy bottomed 2-quart saucepan, combine 2 cups milk, half-and-half, onion, bay leaf, and peppercorns. Bring to a light boil, lower the heat, and simmer on medium-low heat for 20 minutes to allow the onion and spices to infuse into the milk. Using a strainer, strain the infused milk from the onion and spices and return the strained milk to the saucepan. While the milk is simmering, bring a pot of salted water to a boil. Add the elbow macaroni and cook for 4-5 minutes. (This is less time than the package directions. You want the macaroni undercooked. This prevents the pasta from becoming too mushy in the casserole.) Drain, add to a large bowl, and set aside. In a medium bowl, mix the remaining ¾ cup of milk with the cornstarch. Whisk until well combined. Add half the milk mixture in the saucepan to the milk and cornstarch mixture in the bowl and whisk for 1 minute. Add the milk cornstarch mixture back into the saucepan. Bring the entire milk mixture to a boil on medium-high heat. Lower the heat to medium and cook until thickened, about 5-7 minutes. Mixture will be on the thin side. Reduce the heat to low and simmer for 4-5 minutes. Remove the pot from the stove. Whisk in the dry mustard, cheeses, salt, and pepper. Add the cheese sauce to the pasta and mix well. The mixture should look soupy. Pour the macaroni and cheese mixture into the prepared pan. Combine the fresh breadcrumbs and olive oil in a small bowl and mix well. Sprinkle the top of the macaroni and cheese with bread topping. Bake for 20-25 minutes until topping is light brown and macaroni and cheese is bubbly.