In large, microwave-safe bowl, melt butter. This bowl will get VERY hot so make sure you have oven mitts handy! Stir in salt, milk, syrup, and sugar.
Cook for 14 minutes on HIGH in microwave, stirring every 2-3 minutes with a wooden spoon, or until candy thermometer reaches 225 degrees (firm ball).
Stir in vanilla after it is done cooking. Pour into PAM-sprayed 9 x 13 pan and allow to cool at room temp for about 30 min to 1 hour (when pan is no longer hot on the bottom and caramel is cut-able). Using a plastic knife, cut one row of caramel at a time and slice to desired size. (The caramel tends to slide together, thus the reason for cutting only one row at a time…). Wrap in waxed candy papers. Stores well in ziplocs!