When it has reached your desired thickness (saucy and not too thick) add 1 vegetable cube crumbled, 1 tsp dry mustard, dried parsley, salt & pepper to taste.
Now for the cheesy part.... add grated old cheddar cheese until it begins to look like cheese sauce. Depending on how much white sauce you have made will depend on how much grated cheese to use. As a variation, add in other cheeses you like. Even plain or herbed cream cheese works great if you need to use some up!
Make it Gluten Free by using corn starch instead of flour!