What happens next?

How to make buttercream filling
Place the butter in a mixing bowl and beat it until it is smooth and fluffy.
Use a handheld mixer or a food processor with a whisk attachment. It will make things much easier.

Pick from:
A). Remove a small portion of the mixture from the mixing bowl, and transfer it to a mixing bowl. Using the tines of a butter knife, spread the butter to the top of the mixing bowl.;
B). For a richer flavor, use a different kind of butter. Avoid butter with added sugars, as it will make your filling bitter.;
C). Beat the buttercream filling until the mixture becomes light and fluffy. Use a mini setting to beat the buttercream filling.;
D). You can use a whisk or a wooden spoon in a pinch. For a less sweet buttercream, use salted butter.;
D).