Arrange new potato and, if desired, sweet potato in a steamer basket over boiling water.
Cover and steam 20 minutes or until tender.
Rinse with cold water to stop the cooking process.
Arrange green beans in steamer basket over boiling water.
Cover and steam 4 minutes or until crisp-tender.
Plunge into ice water to stop the cooking process; drain.
Repeat procedure with cauliflower, and then broccoli.
Place vegetables on a lettuce-lined platter; cover and chill.