Mac Cheese Sauce

1. Make the rue: melt 1 part butter and then "fry" 1 part flour in it. Corn soup powder base works as flour too.
2. Add the sour cream and mix
3. Add the milk, especially if the base seems to be heating too quickly
4. After stirring well and folding the sauce into itself, start adding diced or shredded cheese and stir until evenly blended
5. Optional: a bit of sugar can help, and tomato paste add more depth and flavor too