Cooking can be both a physical and chemical change. For example, mashing up potatoes is a physical change, but baking a cake is a chemical change.
A physical change is when only the physical characteristics are changed and the substance still remains what it was before the change. Ripping paper, mashing potatoes or freezing water are examples of physical changes because the substances are still paper, potatoes and water after. Chemical changes are when a new substance forms after the change occurs. Baking dough into bread, cooking eggs and burning a steak all produce new substances after the change occurs.