Preheat oven to 350F. Lightly grease a large 4-qt baking dish* and set aside
Combine cheddar and mozzarella cheeses in a large bowl and set aside
Cook the pasta one minute short of al dense
Remove from heat, drain, rinse with cold water and place in a large bowl. **
Drizzle pasta with olive oil and stir to coat pasta. Set aside to cool while preparing cheese sauce
Melt 6 tablespoons of butter in a deep saucepan
Whisk the flour into the butter over medium heat and continue whisking for about 1 minute until bubbly and golden - do not burn!
Gradually whisk in the milk and heavy cream until smooth
Continue whisking until you see bubbles on the surface and then continue cooking and whisking for another 2 minutes
Add in salt and pepper
Add two cups of shredded cheese and stir until smooth
Add another two cups of shredded cheese and continue whisking until creamy and smooth
Add the last couple cups of cheese to the sauce - the sauce will be thick at this point and that's a good thing!
Stir in the cooled pasta until combined and pasta is fully coated with the cheese sauce
In a small bowl, combine panko crumbs, Parmesan cheese, melted butter and paprika.
Sprinkle over the top and bake, uncovered until bubbly and golden brown, about 30 minutes.
Broil in the oven for two minutes if you want a crispier topping.