This is also known as a white sauce. A white sauce can be the starter of many cream sauces or used in casseroles like Tuna Casserole, Pretzel Crusted Chicken, Curry Chicken Divan or as the top layer of a lasagna.
2 tbsp of butter
2 tbsp of flour
1 cup of milk
Heat up the milk at a low temperature on the stove or in the microwave. In a sauce pot over medium heat, add the butter and let it melt. When it's almost bubbling, add the flour and whisk together. Keep an eye on this mixture since it is very easy for the butter and flour to burn at this stage. Let the flour cook out for a few minutes then when it looks doughy, slowly whisk in the milk, keep whisking until the sauce is thickened. This may take 5 minutes.
To make a cheese sauce, when the sauce is thickened, add 1 cup of shredded cheddar cheese and allow the cheese to melt. Pour over steamed broccoli or cauliflower.