Prepare a baking pan covered with baking paper and preheat the oven to 130°.
Finely chop the almonds, setting aside a few whole almonds for decorating the cookies; meanwhile, beat the eggs well in a large bowl. Gradually add the confectioner's sugar to the baking powder, working with a wooden spatula, then complete the dough with the addition of the ground almonds and lemon peel.
The dough will not be very heavy in texture, it will be very similar to that of the macaroons, for those who have made them.
Take small amounts with your hands (make sure that they are small, because they expand while baking), form balls, and place them on the baking pan leaving enough space between them. If you prefer, you can make thick discs with a pastry bag, with a wide round nozzle.
Decorate each ball with an almond and bake in a 130° for about 30 minutes.
Turn off the oven and allow your flourless almond cookies to cool in their baking pan with the oven door open.
Mamma Andrea's flourless almond cookies are very delicate cookies, so treat them accordingly: if they easily pull off the baking pan, that's fine, otherwise use a spatula.
Your flourless almond cookies can be stored in a tin box for a while, but I think you'll eat them right away, also because they are particularly good when fresh out of the oven.