In a medium pot on the stove, combine milk, sugar, and salt and let it come to a boiling point.
Let cook for about 5 min.
Remove from stove and stir in peanut butter and vanilla.
You need a cup of cold water to drip some of the milk and sugar solution that is boiling from a spoon; if you can roll the dough into a ball, its ready.
Pour in a cookie sheet to cool.
Cut into squares and serve!