In a medium saucepan on medium-high heat add both sugars. Stir sugars constantly until they start to melt. They will clump at first, then quickly melt. Be very careful not to burn the sugars.
When the sugars are just melted add the butter and stir to melt and combine. When the butter is fully incorporated add the cream slowly stirring constantly. Let boil for 1 minute watching to make sure the sauce doesn't burn.
Remove from heat. Add vanilla and salt and stir to combine.
Cool at room temperature in a mason jar or glass container of choice. Store in fridge up to two weeks. Slight warm sauce before using. Great on ice cream, in coffee, on top of bars, cake, cookies or anything else you can think of!