Whip the softened butter together until smooth in a large bowl, for a few minutes until super fluffy.
Add in vanilla extract. WHIP again.
IF MAKING CHOCOLATE: Add your cocoa powder next and combine fully before adding in powdered sugar.
Add powdered sugar a ½ cup at a time, not adding NEW sugar, until each batch is fully incorporated. This will ensure you get the creamiest frosting.
Ultimately we want to whip this frosting for at LEAST 7 - 10 minutes.
Slowly stream in a little cream or milk until frosting reaches desired consistency.
Scrape sides and whip again until light, fluffy and smooth, 1 - 2 minutes.
Once your cake is fully cooled, frost away!