Melt butter in a small saucepan until brown specks start to appear.
Whisk in brown sugar and 2 Tbsp. heavy cream. Mixture will start to foam.
Gently whisk for another 2-3 minutes until sugar is dissolved and mixture starts to thicken. Remove from heat and allow to cool.
Stir in powdered sugar and vanilla. Add cream one tablespoon at a time until desired consistency is reached.