Heat the oven to 400°.
Use a food processor to puree the cauliflower in batches.
Pack the cauliflower puree into a glass baking dish and spread to distribute evenly. Bake for 15 minutes.
Allow the puree to cool enough to work with it by hand—stirring with a spoon to facilitate faster cooling.
Scrape the puree onto a flour sack towel or a fine-weave cheesecloth and wrap tightly.
Squeeze the liquid out of the cauliflower over a measuring cup.
(A 2¾-pound head of cauliflower yielded approximately 4 cups of packed, riced cauliflower, approximately 2¾ cups pressed “flour” and 1½ cups of water squeezed from the puree.)