Add the flour and butter to a small sauce pan. Heat over medium heat and whisk the ingredients together until they are combined and slightly thickened. Whisk and cook for about 1 minute.
Then whisk in the milk. Turn the heat up slightly and allow the milk to simmer while you're still whisking. Heat until the mixture has thickened enough to coat a soap. Then remove from the heat.
Then gradually whisk in the shredded cheddar cheese a little at a time until it's all added and well combined. If the cheese sauce is too thicken, gradually add in more milk until the sauce is the consistency that you prefer.
Stir in the salt and then serve immediately while warm and enjoy!