Whisk all-purpose flour, granulated sugar, baking powder, baking soda, and salt together in a large bowl.
Combine buttermilk with melted butter and egg yolks in a separate bowl.
Pour the buttermilk mixture into the flour mixture and stir with a spatula until most of the flour is moistened.
Add the egg whites and fold in just until incorporated, but do not overmix.
Set the batter aside for 10 minutes.
Cube the remaining unsalted butter, take the preheated skillet out of the oven, and add the butter.
Swirl the pan until the butter melts and coats the bottom and sides.
Transfer the pancake batter to the pan, and spread into an even layer.
Sprinkle blueberries evenly over the pancake batter.
Bake the pancake until puffed and golden-brown.
Cut into wedges and serve with maple syrup and more berries.
