Butter the cake pan and set aside. Pour the oat into a pan and roast over low heat, then leave to cool.
Wash the apples, peel each apple, and cut them into four different slices. Then remove the middle part of each slice, then cut it into several smaller slices. When all the apples are cut, sprinkle them with lemon juice.
Separate the egg yolk from the white. Beat the egg white until fluffy, then place in the fridge.
Place the butter(100g) and the sugar into a bowl and mix using a spatula or a hand mixer until you get a homogenous mixture.
Add the egg yolk, the salt, and the zest of a lime to the mixture and mix.
Add the flour, the baking powder, and the oats. Then add the egg white and mix all together. Pour the batter into the cake mould. Preheat the oven to 200°C.
Place the apple slices all over the batter in a circular form, then distribute the almond flakes on it. Cut small pieces of the butter (40g) and place all over the cake.
Bake the cake for 50 to 60 minutes at 175°C until golden brown and a knife inserted in the center comes out dry.