To prepare White Puree:.
On the stovetop, pour about 2 inches of water into a pot with a tight-fitting lid. Put a vegetable steamer basket into the pot, add the cauliflower, and steam for about 10 minutes, until quite tender. Drain.
To prepare in microwave, place the cauliflower in a microwave-safe bowl, cover it with water, and microwave on high for 8 to 10 minutes or until very tender. Drain.
Meanwhile, place the raw peeled zucchini with the lemon juice in your food processor and pulse a few times. Next add the cooked cauliflower and 1 tablespoon of water to the food processor (work in batches if necessary) and puree on high until smooth. Stop occasionally to push the contents to the bottom. If necessary, use another tablespoon of water make a smooth puree, but the less water, the better.
This recipe makes about 2 cups of puree; double it if you want to store more. It will keep in the refrigerator for up to 3 days, or you can freeze 1/4-cup portions in sealed plastic bags or small plastic containers.