Sift flour on the work surface, make a well in the middle of the flour. Pour in 200 grams (approximately 3/4 cup) of sugar, egg yolks and lemon zest. Place butter int the flour edge, knead everything into a ball, wrap in foil and let stand for 1 hour in the refrigerator. Whisk the egg whites with the remaining sugar until stiff and fold in the almonds.
Preheat oven to 200°C (approximately 400°F). Line a baking sheet with parchment paper. Roll out the dough and cut out cookies of 5 cm (approximately 2 inch) in diameter. Add a little almond mixture on top to each, then squeeze the cookies. Brush egg yolk with condensed milk onto cookies, sprinkle with the chopped hazelnuts and bake in the oven for 15 minutes until golden.