Butter can be heated or melted, but should not be overcooked. Above 120°C, it blackens, due to the traces of lactose and protein it contains, thus caramelising. On the other hand the fatty acids in butter are stable during cooking. Which is not the case for vitamins! The ideal way of preserving all the benefits of butter is therefore to have it uncooked, melted on or mixed in other food preparations (e.g. pastries).