Liver and Onions

8 slices bacon (about 1/3 pound)
1 large onion, sliced (about 2 cups)
four 1/2-inch-thick slices calf's liver (each about 3 ounces)
1/2 cup all-purpose flour seasoned with 1 teaspoon freshly ground black pepper
1/4 cup water
1/2 cup ketchup

In a large heavy skillet cook bacon over moderate heat until crisp and transfer with a slotted spoon to paper towels to drain. Pour off half the fat from skillet into a small bowl and reserve. Add onion to skillet and cook over moderate heat, stirring, until golden. Transfer onion with a slotted spoon to a bowl. 

Rinse and pat dry each piece of liver. Dredge liver in flour mixture, shaking off excess. Add reserved fat to skillet and heat over moderately high heat until hot but not smoking. Sauté liver in batches until crisp and browned, about 2 minutes on each side for medium. Transfer liver with a slotted spatula to a platter and add water and ketchup to skillet, stirring occasionally and scraping up bits. Simmer sauce, stirring constantly, 1 minute. 

Serve liver with bacon, onion, and sauce.