In a small to medium saucepan melt butter over medium-low heat.
Once the butter is slighly melted add the milk.
Add the brown sugar and stir continuely untillall butter is melted and sugar is dissolved.
Continue stirring until it starts to slightly boil, stir for a further few minutes or until it starts to thicken.
Remove from the heat and add the vanilla extract
Pour over hot or warm dessert straight away while it is still warm. You can add to cold or room temp desserts such as cakes and slices while it is still warm if you like.Otherwise, let it cool down completely if you are wanting to add it to desserts such as ice cream.