Wash untreated lemon, grate dry and halve. Cut 3 slices from one half. Grate the remaining peel of the halves. Squeeze all lemons and put 2-3 tablespoons of juice aside for the glaze. Whisk eggs and sugar with the whisk of the hand mixer for about 5 minutes until creamy. Mix flour, almonds and baking powder. Fold in lemon juice, lemon zest and flour mixture.
Pour the mixture into a greased, floured box form (approx. 20 cm, 1 1/2 litre capacity) and bake in a preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: level 2) for 50-60 minutes. Remove the cake from the oven, turn out of the tin after approx. 10 minutes and let it cool down on a cake rack. Sieve icing sugar into a bowl and stir with 2-3 tablespoons of lemon juice to a thick icing. Spread the icing on the cake. Halve 3 lemon wedges and almonds and decorate the cake with them. Let the cake dry for about 1 hour
waiting time approx. 2 hours