Peel and cube the sweet potato.
Bring a pot of water to a boil and cook the sweet potato until tender, about 10-15 minutes.
Drain the sweet potato and add it to a blender or food processor.
Add the milk and blend until smooth.
In a saucepan, melt the butter over medium heat.
Whisk in the flour and cook for 1-2 minutes.
Gradually whisk in the sweet potato-milk mixture and cook until thickened, about 5 minutes.
Remove from heat and stir in the cheddar and mozzarella cheeses, salt, and pepper.
Serve the cheese sauce over cooked pasta.
