In a large bowl, beat softened butter with a mixer on medium speed until smooth and creamy (about 2 minutes).
Slowly add powdered sugar, 1 cup at a time, mixing on low speed to avoid a sugar cloud. Scrape down the bowl as needed.
Pour in vanilla extract, salt, and 2 tbsp of heavy cream. Mix on medium-high until fluffy (about 2-3 minutes). If too thick, add more cream (1 tsp at a time).
For stiffer frosting (for piping), add a bit more sugar. For softer frosting (for spreading), add more cream.
Spread or pipe onto cooled cakes/cupcakes.
