For the apple pie, preheat the oven to 180 °C top and bottom heat. Mix yogurt, flour, egg, baking powder, sweetener and cinnamon to a dough.
Cut an apple into small pieces and mix into the batter. Pour the batter into a mold and cut the second apple into thin slices.
Place the apple slices on top of the cake. Sprinkle with a little cinnamon and bake the cake for 25-30 minutes.