Preheat the oven to 175 degrees Celcius.
Line or grease a 20 cm spring form.
Add eggs and stevia granulated sugar to a blender and mix until smooth and a little fluffy.
Add ricotta, apple sauce, vanilla drops and apple cider vinegar and mix until smooth.
In a separate bowl combine oat flour, rice flour, cinnamon and baking soda and mix to combine.
Add in little by little to the wet ingredients and mix until combined.
Fold in the two whisked egg whites, and mix just until combined.
Add the diced apples and gently fold in.
Pour the batter to the prepared spring form.
Top with sliced apples and bake in the oven for 25-35 minutes. The cake is ready when a toothpick comes out clean.
Take out of the oven and let it cool before removing it from the spring form.
Garnish with icing sugar (if using).