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1
Preheat the oven to 375 degrees; butter a 9-inch square baking pan.
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2
Bring a large pot of water to a boil (over high heat); add macaroni and cook 8-10 minutes or until al dente; drain and rinse with cool water.
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3
Place drained macaroni in a large mixing bowl; drizzle with the oil.
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4
In a small saucepan over med-high heat, warm the milk.
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5
In a large saucepan over med-low heat, melt 4 tablespoons butter; sprinkle in the flour and whisk constantly until the flour is absorbed and the mixture is bubbling gently and is lightly golden (2-3 minutes).
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6
Gradually add in the warm milk, whisking constantly.
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7
Increase the heat to medium and bring to a simmer, stirring with a wooden spoon until smooth and slightly thickened.
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8
Add in the cheddar, American cheese and fontina; remove pan from the heat.
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9
Whisk the mixture until the cheese is almost completely melted, stir in the salt, pepper, and mustard.
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10
Pour the sauce over the macaroni; stir to combine.
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11
Transfer mixture to the prepared pan.
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12
In a small bowl, combine the 1/4 Celsius shredded cheddar and the breadcrumbs; sprinkle evenly over the macaroni.
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13
Cut the remaining teaspoon of butter into small bits and dot the casserole.
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14
Bake on the middle rack for 20-25 minutes or until bubbling and a crust begins to form.
