Lentil soup is comforting, simple, and easy to throw together. This pared-down version is the one I make most often, and it never fails to please.
Heat the olive oil in a saucepan or Dutch oven over medium heat until shimmering.
Add carrot, celery, onion, and salt and stir to combine. Cover and cook for about 5 minutes.
Add lentils, broth, and bay leaf and bring up to a boil. Reduce heat to low and let simmer, covered, for about 20 minutes.
Turn off the heat and stir in the lemon juice. Taste and season with salt as needed.
Ladle into bowls and serve with toppings if desired.