Pre-heat the oven to 200° C.
In a large mixing bowl, whisk together the buttermilk, egg yolks and vanilla extract. Add the melted butter and stir well.
Sift the flour, baking powder, sugar and salt together in a separate mixing bowl. Make a hole in the flour mixture and pour the buttermilk mixture in, whisking at the same time to incorporate, but making sure you don't overmix.
Beat the egg whites in a separate mixing bowl until they form soft peaks and fold into the batter.
Arrange some of the blueberries and apple in 4 individual ceramic oval baking dishes. Spoon the batter carefully on top and dot the remaining apple and blueberries on the surface. Bake for 15-20 minutes until golden and set.
Remove from the oven and allow to rest for 5 minutes before serving.