Cook macaroni according to shortest package directions (or one minute less), until nearly tender. Drain well.
Gently stir dry flour into macaroni until just combined.
Add butter, milk, Velveeta, and spices. (If serving immediately, reduce milk to 1 1/2 - 2 cups.)
Cover and cook over low heat, stirring frequently, until melted, thick, and smooth. Add cheddar if desired.
Serve immediately, or put in a crockpot and warm on Low for 2-3 hours.