1. Cut broccoli stalk into 1-inch pieces; separate head into small florets. Place stalk and florets in a vegetable steamer. Steam, covered, 14 minutes or until very tender. Remove broccoli from steamer, reserving cooking liquid.
2. Place broccoli in a food processor; process until smooth, adding cooking liquid, 1 tablespoon at a time, to reach desired consistency. Strain using a sieve or food mill, if needed; discard solids.
You may notice that most of the purees call for steaming rather than boiling. That's because the less water the vegetable or fruit comes in contact with, the more vitamins and minerals the food retains. Some nutrients still leach into the water when you steam, which is why we recommend saving and using the cooking liquid to help smooth and thin your purees.