Place the butter, vanilla extract, and salt in a mixing bowl. Mix on low speed until just combined, then increase the speed and beat until smooth, about 1 to 2 minutes.
Sift the powdered sugar through a fine mesh sieve directly into the bowl. Use the back of a soup spoon to press the sugar through if needed.
Mix on low speed until the butter and sugar are just combined, then increase the speed and beat until light and fluffy, about 1 minute. Scrape down the sides of the bowl with a rubber spatula halfway through mixing. Use immediately, or store in the fridge or freezer for later use.
Notes
If your butter is too cool to mix smoothly, microwave it in 10-second increments at 50% power. It’s ready when it yields slightly under your fingertip.
Mix slowly after adding the icing sugar to avoid a cloud puffing out of the bowl.
Storage
Store buttercream in an airtight plastic or glass container. It can be kept in the fridge for up to 2 weeks or in the freezer for up to 2 months. It can also stay at room temperature for up to 2 days.