In a stand mixer fitted with the paddle attachment, beat the butter for 1–2 minutes until smooth but still slightly cool.
Measure 6 cups of powdered sugar first, then sift it. Add the sifted sugar ½ cup at a time, mixing on low speed between each addition.
Once fully incorporated, add the vanilla, salt, and 2 tablespoons of heavy cream. Beat on medium-high for 4-5 minutes until light and fluffy.
Adjust the consistency: add more cream to loosen or a bit more sugar to stiffen.
For a whiter finish, add a tiny drop of violet gel food coloring to cancel out the yellow tone from the butter and beat until fully incorporated.
Finish by stirring the buttercream by hand with a spatula to press out any air bubbles before using.