Beat sugar, egg whites and juice of one lemon with a mixer (highest speed) for 5 to 10 minutes until creamy. Add 300g ground almond kernels and fold in.
Sprinkle the remaining almond kernels over the surface and roll out the nut dough to a thickness of about one liter. Cut out any shapes and shape on a baking sheet lined with parchment paper.
Bake in a heated oven for about 18-20 minutes (electric oven: l50 °C , convection oven: 130 °C , gas: level 1-2).
Stir the powdered sugar and the juice of one lemon and brush the still hot Guetzli with it. Keep cooled in a tin.