Remove backbone from duck and quarter or bone. Reserve backbone and giblets for broth. Place salt in deep saucepan, add duck pieces and cook for 20 minutes.
Remove duck, placing it in a shallow baking dish. Bake at 350° F for 45 minutes. Increase heat to 375° F during the last ten minutes of cooking. Combine giblets, backbone and water in saucepan and bring to a boil. Reduce heat, simmering for 2 hours. Add onion, celery, garlic and bay leaf to broth; cover and simmer an additional 20 minutes. Strain.
Melt butter, stir in flour and cook for 2 minutes. Add broth and blend, cooking until slightly thickened. Add green peppercorns and season to taste with salt. Serve sauce over duck.
Servings: 4