This is Chef Gabriel Claycamp's (of Culinary Communion) recipe for basic mirepoix. Classically, mixepoix is used in stocks to enhance flavor, aroma, and balance, and is a mixture of 50% onion, 25% carrot, and 25% celery. Stock is a flavored liquid made by simmering roasted bones and aromatics in water. Please note that this is not a recipe designed to make stock, itself, but rather just introduces mirepoix basics. Recipe posted with permission.