Warm 3 tablespoons of the olive oil4 tablespoons in a large Dutch oven or soup pot over medium heat. Once the oil is shimmering, add the chopped onion1, carrot3, celery, seasonal vegetables2 cups and ½ teaspoon of the salt1 teaspoon. Cook, stirring often, until the onion has softened and is turning translucent, about 6 to 8 minutes.