The basis for the creamiest sauces and the lightest cakes, or simply the best thing you can spread on a slice of warm toasted bread.
The traditional way of making butter is to collect milk from several milkings and allowing it to become thick and sour. It is then churned at intervals, (in the old days if the load was big enough the treadmill was powered by a horse or a donkey ). Churning is a process where the cream is thrashed about until the fat globules are freed from the lecithin, a natural emulsifier in milk. The butter is then washed with ice water, molded and wrapped.
It is essential to use untainted milk of the highest quality when making butter in a small scale. In large scale commercial dairies tons of surplus milk undergo several pasteurizations and high speed churning. Artifical flavoring is usually added (none left after all those pasteurizations).
Butter can be made from sweet cream, which gives a mild creamy butter, or from soured cream which produces a slightly acid fully-flavored butter.