
Cardamom bitters is a cocktail bitters flavored chiefly with cardamom, added in dashes for aroma and balance.
Cardamom is a narrow aroma and the bitterness under it is generic, so the two halves come apart easily: the bitterness is replaceable, the aroma only approximately. Whatever you build it from will read as cardamom-adjacent rather than as the bottle.
Angostura plus a pinch of cardamom
Dash for dash the aromatic bitters hold the bitterness, and a knife-tip of ground cardamom puts the direction back. It will not rebuild the exact note, but the drink stands up.
Green cardamom crushed into syrup
Syrup carries the aroma without the alcohol and with sugar attached, so it lands in a different part of the recipe: the sweetening, not the seasoning. Syrup goes in by measure rather than by dash, so the drink’s sweetness comes down.
Cardamom is an essential-oil spice, which means the aroma is volatile and the bottle should be kept tightly closed rather than merely capped. Stored properly it holds its character for years — this is one of the durable ones.