Heat oven to 400 degrees F.
Remove pieces of meat from bones; reserve.
Place bones in large roasting pan.
Bake 1 hour or until bones are well browned.
Add water to bones; stir to remove any browned bits from pan.
Simmer 10 minutes.
Place bones and water in 6-quart stock pot.
Bring mixture to a boil over high heat.
Reduce heat to medium; simmer 4 to 5 hours.
Strain stock; chill.
Place meat scraps from bones in food processor bowl; process until meat is finely chopped.
Combine meat, vegetables, egg whites, peppercorns, juniper berries and bay leaf.
Stir meat mixture into cold stock in 4-quart saucepan.
Bring mixture to a boil.
Reduce heat to low; simmer 2 hours.
Remove any fat.
Stir in sherry; season with salt and pepper.