Melt butter and heavy whipping together in a pot over medium heat. Whisk until they're fully melted and combined. Do not boil.
Remove the pot from the heat and add brown sugar and whisk. Whisk for at least a minute to make sure the sugar dissolves. Use a spatula and scrape the bottom of the pot to make sure all sugar has dissolved. Place back over medium heat and DO NOT TOUCH IT. The bubbles will form on the edge then work to a rolling boil. Once the entire surface reaches a rolling boil, set a timer for 2 minutes.
Take off the heat and add the vanilla. Wait two minutes before stirring the vanilla in. Once the caramel cools enough to work with, about 5-6 minutes, cover the surface with cling wrap.
Let cool and set for 2+ hours. Remove the cling wrap and it's ready to use!