Pull the leaves off the cauliflower and cut out the core in a kind of cone-shaped section. Then pull the florets off the head with your fingers, using a knife when you need to. Break or cut the florets into smaller, regular pieces (about 1 1/2 inch) and put them in the steamer insert. Bring about 1 inch of water to a boil in the steamer pot, add the insert, cover, and cook for about 15 minutes, or until you can poke a paring knife into the stems and you can feel that there’s still a little texture there. Stir the cauliflower well a few times while it’s steaming so that it cooks evenly.
Dump about half of the cauliflower into a food processor. Measure out 3/4 cup of the steaming liquid, and pour in about 1/4 cup; purée until smooth. Now dump the rest of the cauliflower on top, add about 1/3 of the remaining liquid, and purée again. You’ll need to stop and scrape and stir the purée a few times; add more liquid as you need to, but with the understanding that you really want to add as little liquid as you can get away with. With the motor running, process in the butter, salt, and pepper through the feed tube.
Preheat oven to 400 degrees F.
Spread as much of the cauliflower puree onto your pizza crust as you want.
Top with shredded mozzarella cheese, roasted red peppers, and fresh basil.
Bake for 10-15 minutes.
Remove from oven and top with arugula and shaved Parmesan cheese.
Broil for 1-2 minutes. Be careful not to let all the Parmesan cheese melt.
Remove from oven and drizzle balsamic glaze across the pizza. Serve immediately.