Combine brown sugar and butter in a small saucepan and bring to a boil over medium heat.
Allow to boil for 2-3 minutes, whisking occasionally.
Add the cream and whisk, then cook for a minute or two longer.
Whisk in vanilla and remove from heat.
Pour into container.
Use over ice cream.
Store in the fridge when not in use. Microwave for 45 seconds to 1 minute to warm up.