Mirepoix is a French name for a mix of onions, carrots and celery. It is used as a base for stocks, soups, stews and sauces. Some chefs prefer a 2:1 ratio of onions to carrots and celery. Mirepoix can be used raw, roasted, or sauteed. When preparing mirepoix, I like to use "regular" or "conventional" onions but organic carrots and celery. I do this because onions have a fairly low concentration of pesticide residue, while carrots and celery are higher in pesticide residue. Carrots are sometimes on the Environmental Working Group's "Dirty Dozen" list of fruits and vegetables with the highest pesticide residue. This year, celery was ranked the item likely to have the highest amount of pesticide residue. The idea behind the "Dirty Dozen" list and ranking fruits and vegetables is that people can maximize their grocery dollars and minimize pesticide exposure by focusing on buying organic where it can benefit them the most.