In a small sauce pan over medium heat, melt butter.
Add brown sugar, cream and vanilla to sauce pan and whisk until combined.
With a wooden spoon, stir constanty over medium heat until bubbly and thickened (8-10 minutes). The mixture will bubble and foam. The caramel sauce is ready when it coats the back of your spoon and resembles the thickness of gravy as it drizzles. If you have a candy thermometer available, the temperature I look for is 250-275°F.
Remove from heat and allow to cool for 15 minutes.