I rather imagine Mr Snape's cupcakes would be the result of endless experiments on large and smaller quantities of bicarbonate of soda and whether it would improve things to grate the chocolate, shave it, chop it, or dice it before melting it. With endless notations in each cookbook. With the result being the world's most perfect chocolate cupcake that no one else ever makes because their own recipes are just fine and his requires too many charms to keep the temperatures perfect.