Line a baking tray with parchment paper and preheat the oven to 265°F.
Finely grind the almonds, setting aside a few whole almonds for decorating the cookies; meanwhile, whip the eggs well in a large bowl.
400 g peeled almonds, 3 whole eggs
Pour the powdered sugar and baking powder over the egg, and continue to whisk.
400 g powdered sugar, 5 g baking powder
With a wooden spoon or a silicon spatula, fold in the ground almonds, lemon peel, and vanilla extract.
peel of 2 grated lemons or a tsp of lemon extract, 1/2 tsp vanilla extract
The resulting cookie "dough" will not be very dense: it will be very similar to that of macaroons, for those who are familiar with that recipe. Take small amounts of dough with your hands (make sure that they are small, because they expand while baking), roll them into balls, and place them on the baking pan leaving plenty of space in between. If you prefer, you can make thick discs with a pastry bag fitted with a wide round nozzle.
Decorate each ball with an almond and bake for about 30 minutes.
Turn the oven off and allow your flourless almond cookies to cool in the baking pan with the oven door open.
Lift the cookies off the pan gently with 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 because they are particularly good fresh out of the oven.