Melt butter in a medium saucepan on low heat
Add your brown sugar and corn syrup, combine and stir allowing sugar to dissolve and caramelize with the butter- watch carefully as can burn fast
Add the sweetened condensed milk and heat till just slightly bubbling
Remove from heat add vanilla and stir
You can serve immediately (VERY HOT) or place in a small crock pot set on low or warm
Serve with apple slices