onion or 2 tbsp frozen chopped onion

The onion (Allium cepa) is a bulbous perennial plant belonging to the family Amaryllidaceae, native to Central Asia and widely cultivated worldwide. The edible bulb consists of concentric layers of leaf bases that form a compact, underground storage organ with a papery outer skin typically ranging in color from yellow, white, or red depending on variety. Onions are characterized by their pungent, sulfurous aroma when raw, which becomes sweet and mellow upon cooking as the volatile sulfur compounds break down. Key varieties include yellow (the most common, with balanced sharpness and sweetness), white (milder and slightly sweeter), red/purple (sweeter with a mild peppery note), and specialty cultivars like Vidalia and Walla Walla (bred for exceptional sweetness with low sulfur content).

Onions function as a foundational aromatic in virtually all global cuisines, serving as the flavor base for countless dishes from French mirepoix to Asian stir-fries. They are used raw in salads and salsas where their sharp, crisp bite provides textural contrast; caramelized in slow cooking to develop deep umami sweetness; grilled or roasted whole for mild, creamy interiors; and pickled for acidic preservation. Frozen chopped onions are a convenient prepared form used primarily in cooked applications such as soups, stews, casseroles, and sauces where texture preservation is less critical than in raw applications. Their versatility extends to both savory and sweet preparations, and they are essential in building foundational flavors in stocks, braises, and curries.