In a medium saucepan on medium heat, heat sugar, stirring constantly until it is all melted, about 5 minutes.
Immediately add the butter and stir until butter is completely melted, 2-3 minutes.
Slowly add the evaporated milk. The mixture will rapidly bubble when you do this, so be careful. Boil for one minute without stirring.
Remove from heat and stir in sea salt.
Cool to room temperature.
Beat butter on high speed in a stand mixer until light and fluffy, about 3 minutes.
Mix in caramel sauce until fully combined.
Mix in powered sugar a little bit at a time until fully combined.
Spread or pipe on cupcakes, cake, or cookies.
If you follow this caramel recipe, you will have leftover caramel. This is a good thing. Eat it or drizzle it over your desserts!If you use a different caramel recipe or buy store-bought caramel, the caramel will vary in thickness. The caramel recipe here makes a very thin caramel. If your caramel sauce is really thick, increase the amount of caramel in this recipe. I've used as much as a 1/2 cup of caramel when I've used a really thick caramel.