In large bowl, combine flour, baking powder and salt and whisk to blend. Set aside.
In small bowl, beat egg yolks and buttermilk to blend slightly. In another bowl, beat egg whites until foamy, add cream of tartar and continue beating until stiff peaks form when beater is raised. Set aside briefly. Add yolk mixture to flour mixture and mix lightly with a fork until flour is moistened. Stir in cooled, melted butter. Batter should be lumpy. Do not over-mix. Gently fold in beaten egg whites. Preheat skillet. Lightly grease skillet before each batch of pancakes. Pour out batter to make four inch rounds. Quickly drop about six to eight frozen berries onto each pancake. Test for doneness by lifting a corner of a pancake with a metal spatula. When golden brown, turn over and cook about 30 seconds on the other side.. Serve with warmed maple syrup. Makes between 18 and 22 four-inch pancakes. Pancakes may be frozen and reheated.
The Best Blueberry Pancakes
(Can easily halve recipe for fewer cakes.)