Beat the egg yolks. Add chicken fat, salt and pepper, and beat well. Set aside.
Fold matzo meal into egg whites gently, preserving as much air as possible. Fold egg yolk mixture into batter, still preserving as much air as possible. Refrigerate batter 30-60 minutes.
Bring a large pot of water to a boil. Add a generous amount of salt (more than you would use for pasta). Using wet hands, divide batter into 12 portions and form each into a rough ball. Drop into pot.
When all 12 balls are in the pot, and the water has returned to the boil, cover, reduce heat and simmer 30 minutes, turning matzo balls over in the water once. Turn off heat and allow to remain in the hot water for 60 minutes more. Serve in hot soup (or refrigerate up to 2 days, reheating in the soup before serving).