Boil the shells in salted water until just tender, reserve 1 cup pasta water and drain.

Melt the butter over medium-low heat, whisk in the flour and cook for 1 minute without browning.

Whisk in evaporated milk and whole milk and simmer gently for 3 minutes until lightly thickened.

Remove from the heat and stir in Dijon, salt, white pepper, American cheese and white cheddar a handful at a time.

Fold in the shells and loosen with reserved pasta water as needed; serve immediately.