1-1/4 lb. sole fillets
1 onion, chopped
1/2 bay leaf
2 tablespoons lemon juice
3 peppercorns
1/2 teaspoon salt
6 fluid ounces broth or dry white wine
1 lb. fresh spinach
1 tablespoon butter
2 tablespoons flour
1/2 cup skim milk
Salt and freshly ground pepper
1 tablespoon grated Parmesan cheese
Roll up fillets and secure with cocktail sticks. Arrange rolls in pan just large enough to hold them in single layers; add onion, bay leaf, lemon juice, peppercorns and salt. Pour in broth or wine; bring to a boil.
Cover, reduce heat and simmer for 5 minutes. Remove fillets from liquid, reserving liquid.
Wash spinach; cook, covered, in saucepan in just the water clinging to leaves. Drain, and squeeze out excess water; chop finely. Place spinach in shallow greased dish just large enough to hold the fish rolls. Place fish on top of spinach.
Strain reserved poaching liquid; measure 1 cup (add water if necessary). In small saucepan, melt butter; add flour and stir over low heat for 1 minute.
Whisk in poaching liquid, milk, and salt and pepper to taste. Bring to a boil, stirring constantly. Remove from heat. (It may be prepared ahead to this point and reheated.)
Pour sauce over fish and sprinkle with Parmesan cheese. Bake at 375 F for 10 to 20 minutes or until bubbly.