"The satiny texture of this soup will make you think it's cream-based, but it's absolutely dairy-free and delicious! It's a perfect dish to use up leftover broccoli stalks that don't fit into other meals. It freezes well and makes a great winter warm-up snack or lunch! Can be served immediately, seasoned with black pepper, curry powder, or even grated cheese (for people who don't mind dairy) or can be frozen in individual portions and microwaved later."
Heat olive oil in a saucepan over medium-low heat. Add onion and garlic; cook and stir until translucent, 10 to 15 minutes. Add broccoli stalks, potatoes, broccoli florets, and celery root; toss until coated in oil. Cover vegetables with chicken stock; bring to a boil.
Reduce heat and simmer, stirring occasionally, until vegetables are easily pierced with a fork, 20 to 25 minutes. Remove soup from heat.
Fill a blender no more than halfway with liquid and vegetables. Cover and hold lid down; pulse a few times before increasing blender to maximum speed. Puree until soup is light green and creamy, 45 seconds to 1 minute. Repeat with remaining soup, working in batches.