I needed cheddar cheese soup for a recipe and this worked great!
3 T butter
3 T flour
1 cup milk
1 1/2 cup cheese, freshly shredded
Melt butter over medium-low in a saucepan. Add flour and whisk/stir together until smooth. Slowly add milk and continue whisking while bringing mixture to a gentle boil. Once it thickens slightly, add cheese and stir until melted.
This makes about 13 ounces