1. Beat the butter with an electric mixer in a large mixing bowl at high speed until fluffy, about 2-3 minutes.

2. Add half of the amount of sugar and mix on high for about 2-3 minutes. Then, add the remaining sugar and mix on high speed for another 2-3 minutes. Scrape the sides of the bowl to make sure everything is well incorporated.

3. Add heavy cream (for creamy buttercream) or milk (less creamy) and mix again on high speed for 2-3 minutes.

4. Add the vanilla extract and mix again at high speed for 1-2 minutes. Add more heavy cream or milk if the buttercream is too thick and beat again until smooth. If it's too thin, you can add more powdered sugar.