Remove bowl from freezer. In bowl, place row of broccoli with stems toward center of bowl; add row of cauliflower over broccoli, pressing florets to side of bowl. Continue adding cauliflower and broccoli, alternating rows, filling bowl completely. If necessary, drain and discard any excess liquid. Place plate over vegetables; press down firmly. Place heavy can (such as a 28-oz can of vegetables) on plate. Refrigerate at least 3 hours but no longer than 24 hours.