Soften the onion and garlic with the olive oil in a sauce pan. Add the vegetable stock. When it starts boiling, cover and reduce heat to low. Simmer for 5 minutes.
Add the broccoli and simmer until tender (more or less 7 minutes). Add the spinach and let simmer until spinach has wilted. Set aside to cool down and add the basil.
Using a hand blender or food processor, blend until the soup becomes smooth.
Serve soup in bowls and stir in the sour cream into each one.