Melt the butter and brown sugar together in a heavy bottom saucepan. Mix for a couple of minutes until butter and sugar have combined.
Next, slowly add in the heavy cream and stir until the mixture is smooth looking.
Add in the salt and cinnamon, if using, and mix in.
Allow mixture to come to a rolling boil and continue stirring frequently and scraping down the sides.
Continue to stir frequently for about 10 minutes. Take off of heat. Add in the vanilla extract and stir to combine. Pour into heat resistant glass jars. Store in fridge.