cream is churned and creates butter (large clump of fat with some water droplets suspended) and buttermlilk (remaining liquid from the process of churning).
Butter in America must be at least 80% butter fat. Premium butters/European butters can be as high as 86%. Remaining percent is mostly water (13%-19%) and a small percent of milk solids (~1% of proteins, sugars, vitamins, and minerals)
Butter between 34 and 40° F is firm
Flakiness in baked goods is created with firm butter.
As the butter melts in the oven, the fat melts and releases the suspended water as steam which puffs up and separates the different layers.
Butter between 60 and 69° F is softened butter
Ideal temperature is 67° F for creaming with sugar
Whipping sugar into softened butter introduces many air bubbles that are suspended in the milk fat which will expand when placed into the oven.
If the butter is too cold, bubbles can’t be incorporated. Too warm, the bubbles collapse.
Butter between 70 and 89° F is good for spreading
Butter 90° F melts as the milk fat reaches its melting point