In a bowl, mix the butter with the sugar substitute and the maple syrup.
In another bowl, mix the oat flour, almond flour, cinnamon, eggs, baking powder and salt. Pour in the above mixture as well. Stir it up.
If you want, add an apple to your mixture.
Transfer the mixture to a baking tray and place apple slices and the chopped almonds on top.
Put in a preheated oven at 180C for 40-50 minutes.
Cover your pan if it looks like it's going to grab the cake from above.