Mire poix is the cornerstone of stocks and soups. Principally, it uses onions, carrots and celery. Use two parts onion to one part carrot and celery - cut into any evenly-sized shape. Rinse all ingredients thoroughly. Trim and peel onions, and trim off both ends of the carrot and peel. Celery should be trimmed at tip and root as well. Place ingredients in a pan with butter and cook until translucent. You can also substitute onion, celery and carrots for other ingredients - like mushrooms, garlic, leeks, fennel, parsnips, shallots, chilies or tomatoes. Just make sure to stick to a loose 2:1:1 ratio. Variations will give you a white mire poix, a brown mire poix, or a Cajun miro poix.