If you don't have a steamer, simply place the florets in a steaming basket or a metal colander over a large pot of boiling water, and let the steam partially cook them until they are bright green and tender-crisp, about 12 minutes. Cook time will vary so keep your eye on it and test for tender-crisp status with a fork. You don't want the broccoli tender, because it will continue to cook and tenderize while it's in the oven.