Preheat ove to 400 degrees.

Melt butter in a frying pan. Stir in sugar and cinnamon, then add apple slices and cook over low heat for 3 minutes until slices are well coated.

Beat vanilla, flour, egg yolks, and milk together. In a separate bowl, beat egg whites until stiff, then gently fold egg yolk mixture in.

Pour apple slices into an 8 1/2-inch buttered round cake pan. Pour batter over the apple slices and spread with a rubber spatula. Bake for 20 minutes, until the pancake is brown and puffy.

Loosen sides. Place a plate over cake pan and invert. Cut the pancake into wedges and serve with maple syrup, ice cream or yogurt.