Start with preparing the lemon.
Thoroughly wash the lemon and place it in a small pot. Cover the lemon with enough water and cook on a gentle heat until the skin turns soft. It shouldn’t take more than 30 minutes.
Take your lemon out and leave on the side to cool down.
Cut the cooked lemon lengthways in half and search with your fingers for any seeds, which you will discard.
Blitz the quartered lemon into a smooth purée using a hand blender.
Toast the almonds in a pan for a few minutes.
Once they cool down a little blitz them in a blender with the amaretti biscuits and two tablespoons of sugar until all the ingredients turn into a sandy consistency.
If you choose to use already ground almonds, finely crush the amaretti biscuits and mix them with the almond flour.
In a large bowl whisk the egg yolks with the sugar until pale.
Add the ground almonds, amaretti biscuits, a pinch of salt and stir very well. Finally add the lemon purée and stir it into the egg and almond mixture.
In the meantime add a drop of lemon juice to the egg whites and whisk them until they start to form soft peaks.
First fold a third of the whisked egg whites into the lemon and almond mixture and next fold in the rest, making sure you don’t overwork it.
Grease and line with a baking parchment a tall spring form tin, 18 cm in diameter.
Pour the cake batter into the prepared baking tin and even out the surface.
Loosely place a sheet of aluminium foil on top and bake for about 40 minutes in the preheated oven to 175-180 C (non fan).
Take the aluminium sheet off and allow an extra 2 minutes for the cake to turn slightly golden on top in the oven.
Take the cake out from the oven and wait until it cools down before handling.