Mirepoix

A mirepoix is a mixture of diced vegetables, traditionally onions, carrots and celery in a two to one to one ratio, cooked slowly in fat such as butter over low heat without coloring or browning, so as to sweeten rather than caramelize the vegetables. It serves as a foundational flavoring base in French cuisine for stocks, soups, stews and sauces; adding tomato puree to a mirepoix creates a darker variation called pincage.