Cup of Yum
1. Place the butter in the bowl of a stand mixer. With a whisk attachment, whip the butter until creamy and white in color - about 5 to 10 minutes on high speed. You can also do this step with a paddle attachment for fewer air bubbles, but it must be creamed for longer and the volume of the buttercream will then be less (less air).
2. The butter must be fluffy, creamy, and be a very light, almost white in color at this stage. Make sure to scrape the bottom AND sides of the bowl so that there are no butter lumps.
3. Add the salt, vanilla, and about 30 mL / 2 tbsp of the cream (or slightly more for double batches), and whisk further until the butter-cream mix has mixed in very well and is light and fluffy. Again, make sure there are no butter lumps in the mixture.
4. Lower the speed and add 226 g / 8 oz of the confectioner's sugar (same amount as the butter) - a little at a time, and incorporate all of the sugar into the butter. Make sure to scrape the sides and bottom of the bowl as you go.
5. Once the sugar is incorporated into the butter, increase the speed and whisk on high for a few minutes.
6. Taste and add the rest of the confectioner's sugar if needed. Whisk for a further 2 - 3 minutes until you have a light, fluffy, soft, spreadable buttercream.
7. If the frosting is too stiff, you can add up to 2 more tbsp of heavy cream to get an even softer buttercream. Skip this step if you live in a very hot climate though.

For a smoother buttercream with fewer air bubbles

1. The less air that is incorporated into the buttercream, the fewer bubbles will be present in it. This can be achieved by using a paddle mix to make the buttercream, but the process will be slightly longer then.
2. Another method (heat and mix method) is to take a small portion of the buttercream and heat it in the microwave until it has JUST melted. Mix this portion in with the rest of the buttercream in the bowl using the paddle attachment. The buttercream mix will deflate very slightly, but this is expected.