in heavy 5 quart pot/ saucepan, combine milk, corn syrup, sugar and butter. cook over medium heat, stirring constantly until the sugar is dissolved and the mixture comes to boil.
continue to cook, stirring constantly, to 284 degrees on the candy thermometer (or forms a firm ball when a little is dropped into ice water) Remove from heat add vanilla
Pour into prepared pan and let cool to lukewarm, then score deeply with a sharp knife. Let completely cool and cut the pieces out.
*****Ok as you know this takes a while to make. DO NOT put the heat past medium, the candy won't taste as good. Don't stop stirring and get along the bottom and sides as much as possible,cause no one likes burnt caramel. Also found a good pizza cutter, one with a non stick coating, works good in helping cut the caramel. Don't let the caramel sit in the pot too long or you'll be cutting it out of the pot instead of a cookie sheet.