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

Melt butter over medium-low heat, whisk in flour for 1 minute and gradually whisk in milk and cream.

Simmer gently for 3 minutes, then remove from heat and melt in cream cheese.

Add white cheddar a handful at a time and season with salt and white pepper.

Fold in shells and loosen with reserved pasta water until glossy and spoonable.