1. Place green beans in a vegetable steamer. Steam, covered, 15 minutes or until very tender. Remove beans from steamer, reserving cooking liquid.
2. Place beans 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.