Heat the granulated sugar in a medium saucepan over medium heat, stirring constantly until it melts and turns amber.

Remove from heat and stir in the butter until fully combined.

Slowly add the heavy cream while stirring. It will bubble—continue stirring until smooth.

Add vanilla extract and sea salt. Let caramel cool completely.

In a large bowl, beat the butter until fluffy (3–5 minutes).

Gradually add powdered sugar and mix until smooth.

Add the cooled caramel to the buttercream and beat until fully incorporated and fluffy.