* Leek or Green Onion should be finely chopped.
Wash the lentils thoroughly. In a 2 1/2-quart saucepan bring 6 cups of water to a boil. Add the lentils, bacon, leek or green onion, carrot and celery. Simmer, partially covered, for 30 to 40 minutes. Meanwhile in a fry pan, saute chopped onion in vegetable oil until soft. Sprinkle flour over onion, and stir. Lower heat, stir constantly, and cook until the flour turns a light brown. DO NOT burn flour. Stir in 1/2 cup of hot lentil soup into the browned flour; beat with a wire whisk until well-blended. Beat in vinegar. Add contents of fry pan to lentil pan and stir together. Cover and simmer for 30 minutes or until lentils are soft.
Add the frankfurters and catsup. Cook to heat frankfurters through. Season with salt and pepper and serve hot.