Using a stand mixer fitted with a paddle attachment, beat butter on medium high speed for 1-2 minute until pale and fluffy. Scrape down the sides.
Turn off the mixer and add in sifted confectioner's sugar, 1 cup at a time. Turn mixer on low, incorporate the sugar, turn off and add another cup, repeating until all the sugar has been incorporated. Scrape downtime sides in between mixing.
Add in the cream, vanilla bean paste and salt. Mix on medium high, for 7 minutes, until frosting becomes light and fluffy. Seven minutes adds in plenty of air so the buttercream is light and fluffy and easy to spread.
If the frosting is too stiff, add in more cream, one TBSP at a time. If it is too loose, add in more sugar.
Spread on a completely cooled cake with an offset knife for best results.