Bring a large pot of salted water to a boil. Add carrots and cauliflower and cook for 5 minutes, or until tender. Remove from water with a slotted spoon and place in a high speed blender along with ½ cup of the cooking water. Blend until smooth and set aside.

Drain the pot, add butter and set over low heat. Once melted, add flour, salt and pepper. Cook butter and flour mixture for 2 minutes, or until it is golden brown and smells nutty. Increase the heat to high, add the milk, water and pasta, and bring to a boil, then reduce heat to a simmer. Cook, stirring frequently, for 15 minutes, or until the pasta is tender and the milk has reduced to a thick and creamy sauce.

Remove from heat and stir in the blended carrots and cauliflower and the cheddar cheese. Stir until the cheese has melted and everything is well combined.