Chop your vegetables. The size you choose to chop your onions, carrots, and celery will vary depending on the recipe being prepared. However, as a general guideline: for sauteed recipes, chop small (¼-inch to ½-inch), for soups and stews, medium size (½-inch to 1-inch), and for stock, broth, or blended soups, larger size (1-2 inches).

Cook vegetables over medium-low heat. Add about 2 cups of water to a large skillet set over medium-low heat. Add the onions, carrots, and celery. Cook, stirring often, for 10-12 minutes, or until softened and onions are translucent. You may need to add more water over the course of cooking.