Chop onion. Clean leeks and slice white and light green parts only. Chop potatoes (no need to peel).
Meanwhile, Cut broccoli into florets, peel the stem and cut into bite sized pieces. Add the broccoli and peas to the pot, cover, return to a boil, then lower to a simmer and cook for 10 more minutes, or until potatoes and broccoli are soft, stirring occasionally.
Mix in the olive oil or butter, remove from heat, and remove and discard bay leaf. Allow to cool slightly, then blend with a stick immersion blender* and puree.
Return soup to saucepan and reheat gently. Add salt and pepper.**
*Soup may also be removed from the pot and pureed in a blender. Use caution when doing this.
**take into account if your stock is already salted, added salt will be less than ¾ teaspoon.