Cassia (though it's not technically true cinnamon).
Warm, tingly, sweet cinnamon is a spice recognized by just about anyone who has enjoyed French toast, a snickerdoodle, or an aptly named cinnamon bun. But is the spice true cinnamon or its more common relative, cassia? Only your spice merchant knows for sure; often both are labeled and sold as cinnamon. Made from rolled, pressed, and dried tree bark, both cinnamon and cassia have a pleasing, woody fragrance and sweet flavor in both stick and ground form.
The widely available brands tend to be made from cassia (Cinnamomum cassia). For cassia, look for names such as Korintje (from Indonesia) or Saigon cinnamon (from Vietnam), varieties that tend to possess the fullest and finest flavor. The best true cinnamon (Cinnamomum zelanicum) comes from Ceylon and India.
While ground cinnamon may be added right to a batter, pie filling, or streusel topping, whole cinnamon sticks are best for infusing subtle flavor into liquids like custard sauce, hot cider, and poaching syrups.
When fresh, cinnamon should pack an aroma that beckons you to use it. Store in a cool, dark, dry place, and its fragrance should last a year or two.