What is the most common vegetable used as a base for mirepoix?

The vegetable most commonly used as a base for mirepoix is onion. Mirepoix typically consists of a combination of onions, celery, and carrots, with onion serving as the primary component due to its flavor profile and ability to provide a savory foundation for a wide range of dishes. The sweetness of onions develops during the cooking process and enhances the overall depth of flavor in soups, stews, and sauces.

Other vegetables like celery and carrots are also essential for balance in mirepoix, but they generally play supporting roles in terms of flavor. Garlic, although frequently used in many culinary preparations, is not a traditional component of mirepoix and is usually treated as an aromatic added later in the cooking process for enhanced flavor.