Ground the zest of the two lemons and squeeze them for the juice. Set both apart.
Peel the apples without cutting them and then – with a mandoline slicer or knife – cut the apples in very thin slices over a bowl. Add the Lemon juice and mix. The apples don't get brown this way.
Preheat the oven to 180°C/350°F.
In another bowl add the eggs and the sugar. With an electric hand mixer mix until the mixture is a little fluffy and brighter. Now add the lemon zest, the pinch of salt and slowly the flour and baking powder. Mix well for a minute.
Now transfer the batter into the bowl with the sliced apples. Be careful not to break the apples slices.
Prepare a 18 cm/7" round cake pan with parchment paper or grease the inside and put some flour in order to prevent the cake to stick on the rim.
Transfer into the oven and bake for 30 – 40 minutes. After 30 minutes check with a toothpick if the inside of the cake is still wet. Let the cake in the oven for some additional minutes.
Take the cake out of the oven and let it cool in the cake pan. Open the cake pan and transfer the cake on a cake plate. Decorate with some icing sugar.
Instead of the all purpose paleo flour you can use also half-half of almond flour and cassava flour.
I would recommend parchment paper instead of ghee/coconut oil and flour. It is not that easy to transfer later the cake from the baking pan to a plate. With the parchment paper it is easier to lift it.
Instead of icing sugar you can use also sprinkled chocolate for example or simply omit decoration. It looks good also with none.