Scrub potatoes. Cut larger potatoes into quarters. Place in steamer basket over boiling water. Cover; steam for 12 to 15 minutes or until just tender.
In a medium saucepan, cook onion in butter or margarine until onion is tender, but not brown. Add flour and stir until smooth. Stir in the salt, black pepper, cloves, nutmeg, and bay leaf. Add the milk all at once. Cook and stir until thickened and bubbly. Stir in the Gruyere and Parmesan cheeses. Heat and stir until cheeses melt. Remove and discard the bay leaf.
Arrange potatoes on individual plates or in a serving bowl. Spoon the sauce over potatoes. Makes 6 servings.