Closely related to cassia and true cinnamon, Vietnamese or Saigon cassia-cinnamon is harvested from the young branches of the Cinnamomum loureirii tree. Its high essential oil content (up to 8 percent) makes it the most potent of the cinnamon varieties. This intensity doesn't work in all dishes, but when you want a rich, dark, vibrant flavor, there is no match.
Vietnamese cassia-cinnamon is a key ingredient in phở (Vietnamese beef and noodle soup). It also bumps up the flavor and aroma of baked goods, or any other dish where you'd use cinnamon. Use it full-strength if cinnamon is the primary note, or reduce the usual amount for a lighter level of sweetness and pungency.
Related: Video: Cinnamon from Spices of Life