Bechamel, also known as white sauce is one of the mother sauces. It is a simple sauce to make, but it does require you to move quickly and be watchful. You will see it used as a base to other sauces, including cheese sauce for mac & cheese.
Bechamel Sauce
Ingredients and Process
5 tbsp unsalted butter
5 tbsp flour
4 cps milk
1-1/2 tsp sea salt
1/2 tsp white pepper
1/8 tsp nutmeg
Heat up the milk in the microwave until it is very hot, you’ll be able to see vapors rising up. Keep it hot. In the meantime, in a medium saucepan melt the butter over medium heat until there is foam on the top. Add the flour at once, and stir quickly with a wire whisk. This will make a roux, however, you want to keep the mixture light in color–bechamel sauce is a white sauce. 
You need to allow the flour to cook, otherwise the raw flavor will come through in the sauce. The process of making the roux, will take about 6 minutes and will be lightly golden.
Add the milk as quickly as you can, while still whisking it in to avoid lumps. Once you have incorporated all the milk, season the sauce with salt, pepper and nutmeg. Continue to stir until the sauce thickens, it will take about 15 minutes to achieve the consistency of soft yogurt. Remove from heat and allow to cool.