Heat the olive oil in a large pot over mediumheat. Add in the onion and garlic and sauté for 2-3 minutes until fragrant.
Add in the carrots and celery and sauté for an additional 5 minutes.
Add in allremaining ingredients excluding garnishes. It is OK if the broccoli is not completely submerged in the liquid; it will sink / you can push it down as it cooks.
Bring liquid to a boil, then reduce heat tosimmer. Simmer for 30 minutes until broccoli and lentils are soft.
Using an immersion blender, or in 3-4 batches in a regular blender, puree the soup until smooth. (Only fill the blender halfway each time and be sure to start on a low setting and slowly increase, opening vent in lid to allow steam to escape.)
Return to pot over low heat and add additional salt & pepper to taste.
Plate up and top with a dollop of sour cream and sprinkle with chopped green onion. Enjoy!