Ingredients (makes 8 cups)
Heat the olive oil in a soup pot over medium-high heat, and saute the onion, garlic, celery and carrots for about 7 minutes.
Add the broth, lentils, diced potato and tomato paste. Turn the heat up to high until the soup boils. Then, reduce the heat to low and simmer for around 45 minutes or until the lentils are soft.
Mix the corn starch into a small amount of water (around 1/2 cup) and stir the mixture into the soup. Let the soup simmer for 5-10 minutes longer to thicken up. Add salt to taste.