Bring first 2 ingredients to a rolling boil in a 3 1/2-qt. saucepan over medium heat, whisking constantly.

Stir in cream, and return to a boil; remove from heat. 

Pour into bowl of a heavy-duty electric stand mixer. 

Gradually beat in powdered sugar and vanilla at medium speed, using whisk attachment; beat 7 to 10 minutes or until thickened. Use immediately. 

Sprinkle frosted cake with sea salt.