New England Fish Bake

4 medium potatoes, peeled
1 teaspoon all-purpose flour
1 small onion, sliced into rings
1/2 teaspoon salt
1/4 teaspoon pepper
3/4 cup milk, divided
1-1/2 pounds cod fillets or freshwater fish (trout, catfish or pike)
3 tablespoons grated Parmesan cheese, optional
2 tablespoons minced fresh parsley or 2 teaspoons dried parsley flakes
1/4 teaspoon paprika 
 
Place potatoes in a saucepan and cover with water; bring to a boil. 
Cook until almost tender; drain. Slice 1/8 in. thick; place in a greased shallow 2-qt. baking dish. 
Sprinkle with flour. 
Top with onion; sprinkle with salt and pepper. 
 Pour half of the milk over potatoes. 
Place fish on top; pour remaining milk over fish. 
Sprinkle with Parmesan cheese if desired. 
Cover and bake at 375° for 20-30 minutes or until fish flakes easily with a fork. 
Sprinkle with parsley and paprika.