First of all, prepare the shortcrust pastry: put all the ingredients in a bowl and knead them quickly until a homogeneous dough is created, then let it rest in the fridge for at least 30 minutes (even if there is no butter, it is good that the gluten mesh cools and spread out, so that your pastry is more crumbly).

Then start preparing the cream: Whip the butter with the sugar until you get an ointment consistency, then add the eggs and finally the almond flour.

Also add the lemon peel, transfer the mixture into a saucepan and cook over low heat (stirring constantly) to make it thicken until it reaches a boil: in the end it must have a consistency similar to that of custard (but less smooth due to the almond flour).

Take the shortcrust pastry back, divide it into 2 parts (one a little larger than the other) and roll them out into two thin sheets on the lightly floured surface: with the larger half line the previously greased and floured mold.
Level the edges, prick the bottom and fill with the cream.

Close with the second shortcrust pastry disc (sealing the edges well), brush with lightly beaten egg and sprinkle with brown sugar, then cook for about 35-40 minutes at 160 ° C, in a pre-heated ventilated oven.

The frangipane cake is ready: let it cool completely before serving.