1) In a bowl, melt butter (for about 1 minute in the microwave).
2) Add flour along with salt to the melted butter. Gradually add milk and mix the contents well.
3) Cook the contents for about 7 minutes, till the sauce thickens (stir the contents continuously during this process, so that the flour does not lump).
4) This white sauce tastes best with fish, bacon or vegetables.