2 cups chopped onion 1 cup chopped celery 1 cup chopped carrot 2 table spoons butter salt and fresh pepper fresh herbs coarsely chopped parsley, thyme, and marjoram and favorites. Heat a large skillet of sauteed pan over medium heat. Once hot, add butter. Once melted add remaining ingredients and sauteed gently over medium heat until the vegetable soften. Water can be added to this to form a simple stock. Try starting your favorite soups, stews and casseroles with this base, adding ingredients to the finished mirepoix. A mirepoix is used either to season stews, soups, sauces, and fricasses or as a base for braising meats or fish. In this recipe, mirepoix refers to equal parts of finely diced carrot, onion, and celery.