In a 12-inch skillet, cook bacon until done, but not crisp. Drain bacon on paper towels, reserving drippings in skillet. Set bacon and drippings aside.

Trim fat from meat. Cut into 6 to 8 rectangular pieces. Place each rectangle between 2 pieces of plastic wrap. Using the flat side of a meat mallet and working from center to edges, pound each piece of steak to 1/4-inch thickness. Remove the clear plastic wrap.

Spread top of each rectangle with 1 teaspoon mustard and sprinkle with the chopped onion. Place a slice of bacon across the center of each piece of meat. Place a pickle slice across the narrow end of each piece. Roll meat around the pickle. Tie the beef rolls at each end with heavy cotton cord.

In the reserved bacon drippings in the skillet, brown beef rolls over medium heat, turning to brown evenly. Transfer beef to a plate.

Carefully pour the water into the skillet and bring to boiling, scraping up browned bits in the skillet. Add the celery, leeks, parsley, and salt. Add the chopped parsnip, if you like. Return beef rolls to the skillet. Reduce heat and simmer, covered, about 1 hour or until meat is tender, turning beef rolls once or twice during cooking. Transfer the meat rolls to a heated platter and keep warm.

Strain the cooking liquid and vegetables through a fine sieve, pressing on vegetables; discard vegetables. Measure liquid (you should have about 3 cups). Return vegetable broth to the skillet and boil briskly about 10 minutes or until the sauce mixture is cooked down to 2 cups. Remove the skillet from the heat.

In a small saucepan, melt butter over medium heat. Stir in flour. Cook over medium-low heat until mixture begins to brown. Gradually add the reduced vegetable broth, beating vigorously with a whisk until sauce is smooth and slightly thickened. Season to taste.

Pour some of the sauce over beef rolls; pass remaining sauce. Garnish with apple wedges and parsley sprigs, if you like. Makes 6 to 8 servings.