Cook the pasta: Bring a large pot of salted water to a boil. Cook pasta until just al dente, then drain, reserving 1/2 to 1 cup of the pasta water. Set pasta aside.
Steam the veggies: In the same pot or a steamer basket, steam the cauliflower, squash, carrots, onion, and garlic until very tender, about 10–12 minutes.
You should be able to easily pierce them with a fork.
Blend the sauce base: Add the cooked veggies to a blender with milk and broth (or pasta water). Blend until completely smooth and silky. If it’s too thick, add a splash more liquid.
Enrich and season: Pour the blended mixture back into the pot over low heat.
Stir in butter, cream cheese, salt, ground mustard, and paprika or turmeric. Heat gently until melted and smooth.
Add the cheese: Turn the heat to low and stir in shredded cheddar a handful at a time until fully melted. Avoid boiling, which can make cheese grainy.
Taste and adjust salt and pepper.
Combine with pasta: Add the cooked pasta to the pot and stir to coat. If the sauce seems thick, loosen with a bit more milk or reserved pasta water until creamy.
Rest and serve: Let the mac and cheese sit off the heat for 2–3 minutes to thicken slightly. Serve warm.
For extra appeal, top kids’ bowls with a tiny sprinkle of cheese.