Butter is made from churning cream and is a kitchen essential. Without it, cakes, biscuits and pastries wouldn't have the same melting richness and tender texture. It's also used in many classic sauces, such as beurre blanc, beurre noisette, beurre meunier and hollandaise. Added at the end of cooking, it gives richness and gloss to sauces. With a fat content of 80 per cent, butter isn't exactly diet food, but a little goes a long way.
Butter labelled as 'salted' contains three per cent or more salt; the salt was traditionally added to butter to help preserve it. Salted is best for spreading rather than cooking, allowing the cook to maintain control of the seasoning. 'Slightly salted' butter contains 1-2.5 per cent salt and is more versatile than salted.
Butter substitutes such as margarine and 'non-dairy spreads' vary in fat content, water content and flavour. 'Hard' margarine has the same fat content as butter, so is the best 'substitute' for butter - although your baked goods won't taste the same. Because it has the same fat content as butter, it isn't a low-fat option. Low-fat spreads cannot be used as butter substitutes in cooking.
Because butter contains milk deposits it can burn easily, so it can be a temperamental cooking medium. Adding some oil (which burns at a higher temperature) to the cooking pan with the butter can help get around the problem. Alternatively, clarifying the butter will make it more stable. For baking, pale, creamy unsalted butter (sometimes called 'sweet' butter) is better than unsalted butter as it allows the cook to control the amount of salt going into the finished dish.
You can make your own butter at home with just cream and a jam jar. This activity will take a little patience and some stamina in the arms as you shake and shake the cream in a jar, but it will all be worthwhile when, quite suddenly, you're shaking a lump of butter.