To prepare the almond biscuits, pour the whole, peeled almonds into a blender equipped with steel blades. Add the sugar and process both into powder. Put the powder in a bowl. Add the egg white, the grated lemon zest and the almond flavor. Mix the ingredients with the hand mixer until the dough is soft but compact.
Slightly moisten your hands and shape the dough into small balls of approx. 20 - 35 g. Roll the balls in powdered sugar and place on a baking sheet lined with baking paper. Gently squeeze the balls on the upper side with your thumb, index finger and middle finger. Let the almond biscuits rest in the refrigerator for at least 5 hours or overnight.
Preheat the oven to 180 degrees and bake the biscuits for about 12 minutes.