In a medium bowl, combine potatoes, sour cream, onion, if desired, and flour. Add eggs and salt and pepper to taste, mixing well.
Heat oil or melt butter or bacon drippings in a large heavy skillet (or skillet liberally coated with non-caloric vegetable cooking spray) over moderate heat. Spoon ¼ cup potato mixture into skillet for each pancake and flatten carefully to make a 3-inch diameter cake. Cook each until browned on both sides, turning once, total cooking time about 8 minutes.
Keep cooked potato pancakes hot in a preheated very very slow oven (100 degrees F.) while preparing additional pancakes.
Variations: Add 1 to 2 tablespoons chopped chives or minced parsley to pancake mixture.
Add 2 to 3 tablespoons shredded cheese of choice to pancake mixture.
Add 1 to 2 tablespoons crumbled crisp-cooked bacon to pancake mixture.
Add 1 to 2 tablespoons drained diced pimento to pancake mixture.