In a separate pan make a "rue" by melting 1/3 cup butter with just a bit less than 1/3 cup of flour till it's a thick paste. Add in about 1 1/2 cups of milk and warm until it's combined, melted and thickening.
Then add in 1 cup of shredded cheddar cheese or 3-4 cheese slices. If any clumps are there just take them out with a fork.
Add in macaroni stir and eat immediately or you can put in buttered casserole dish and then top with more shredded cheese and bake till cheese melts. I tend to use less cheese this way.