Wash the broccoli florets under cold running water. Put into a saucepan of freshly boiled, filtered water. Bring to the boil, cover, then lower the heat and simmer for 4-6 minutes, or until tender (test stalks). Remove from the cooking liquid and puree to the smooth texture in a blender, or food processor, adding some of the cooking liquid to get the right consistency. Allow the mixture to cool.