<human>: What is the best way to: How do I cream butter to make butter cookies?

OPTIONS:
- To cream butter for butter cookies, mix the butter, sugar, egg yolk, vanilla and salt in a mixer until liquid.
- To cream butter for butter cookies, mix the butter, sugar, egg yolk, vanilla and salt in a mixer until light and fluffy.
<bot>: To cream butter for butter cookies, mix the butter, sugar, egg yolk, vanilla and salt in a mixer until light and fluffy.