Add olive oil to a large pot over low to medium heat and cook the onions until completely caramelized. This may take up to 45 minutes.
Next, add in the carrots, celery, and garlic and cook for 5-6 minutes over medium heat until very lightly browned and tender.
Stir in the cumin and coriander until combined with the vegetables.
Pour the rinsed lentils, potatoes, bay leaves, and chicken stock and stir to combine.
Add a lid and cook over low to medium heat for 35-45 minutes or until the lentils are very tender.
Remove the bay leaves and then using a hand immersion blender, pulse blend the soup until about half of it is pureed. This will help thicken the soup.
Adjust the seasonings of the lentil soup with salt, pepper, and freshly squeezed lemon juice.
Garnish with fresh chopped parsley.
Notes
Make-Ahead: You can make this soup up to 1 day ahead of time. When ready to serve, simply reheat on the stovetop in a pot.How to Store: Cover and keep it in the refrigerator for up to 5 days. This will freeze well covered for up to 6 months. Thaw in the refrigerator for 1 day before reheating.How to Reheat: Add the desired amount to a pot and heat up over low heat until hot. Adjust seasonings with salt and pepper and add a ¼ cup of chicken stock at a time if it is too thick and needs to be thinned out.You can use red, green, brown, or yellow lentils in this recipe, although the color of the soup will change depending upon which one you chose.If you are using a blender to blend the soup, remember to take that centerpiece of the blender lid off and replace it by putting a towel right over the top of the whole while blending.You can substitute the potato for a few red new or Yukon gold potatoes.