Preheat the oven to 350°F.
Lightly grease the baking dish with a Tablespoon of butter until the bottom and all sides are well coated. Set aside.
Using a box grater, shred the sharp cheddar cheese and set aside.
Next, bring a large pot of water to a boil and cook the elbow macaroni to al dente.
When the pasta is done, drain, and place the cooked pasta in a large bowl.
Drizzle the pasta with the 1 Tablespoon of olive oil and stir to coat. Set aside to cool.
In a deep sauce pan, melt the 6 Tablespoons of butter.
Slowly whisk in the ⅓ cup of flour, 1 teaspoon of ground mustard, 2 teaspoons of salt, and ½ teaspoon of black pepper for about 30 seconds until a paste (also called a roux) forms.
Slowly whisk in the milk and heavy whipping cream until the mixture is smooth and there are no lumps.
Continue to whisk on medium-high heat until you small bubbles start to surface. Continue to whisk for 2-3 more minutes until the mixture slightly thickens.
Add 2 cups of shredded sharp cheddar cheese and 1 cup of Gruyère cheese into the mixture and whisk until smooth.
Add another 1 cup of shredded sharp cheddar cheese to the sauce and mix until smooth. The sauce should be slightly thick.Expert Tip: Taste the sauce during this step and add more salt, if needed. Next, add the cooked pasta into the pot of cheese sauce and stir until well combined.
Pour half of the macaroni and cheese into the prepared baking dish.
Sprinkle on the remaining 1 cup of shredded sharp cheddar cheese and 1 cup of Gruyère cheese, and then pour the remaining macaroni and cheese on top of the shredded cheese. Set aside.
It's now time to make the Panko-parmesan crust. In a small bowl, combine 1 cup of Panko breadcrumbs, ½ cup shredded Parmesan cheese, 4 Tablespoons of melted butter, and ¼ teaspoon of smoked paprika.
Sprinkle over the top of the mac and cheese and bake uncovered for 30 minutes. You'll know it's done when it becomes bubbly and the top is golden brown.
Serve immediately.