Cassia buds are the dried, unripe, unopened flowers of the cassia (cinnamon) tree. They look a lot like cloves, but their flavour is like a more floral, peppery cinnamon. They can be ground to a powder with an electric blade grinder, but they are usually used whole to infuse their flavour. Most traditionally, cassia buds are called for in some pickle recipes and certain European pastries and breads. They can also be used in mulling spice blends and other tea-type infusions. Essentially, anywhere that you might use cinnamon sticks or chips, you can substitute cassia buds for a more nuanced and peppery flavour.