Curry powder is not one spice but several spices blended together to make a spice mix. Most jarred curry powders have been sitting on the supermarket shelves and have lost their intense flavor and fragrance. The best curry powder you can have is the one you make yourself. Purchase whole spices (from an Indian market, online, or other food's store) and toast them to release their oils. Blend the whole spices in a coffee grinder (not in the same one that you use for your coffee) or mortar and pestle and store in an airtight container in a cool dark place. DIY curry powder is guaranteed to be the best spice blend you've ever tasted.