Chop the couverture, melt it over a warm water bath and let it cool down a little. Wash two lemons hot and grate the rind of both lemons finely. Squeeze 1 lemon.
Separate eggs. Beat butter and sugar with the whisks of the hand mixer until creamy. Add egg yolk and lemon peel and stir for 3-4 minutes until creamy. First stir in melted chocolate coating, then lemon juice (approx. 5 tbsp.). Fold in ground almonds.
Beat the egg white until stiff, adding 2 tbsp. sugar at the end. Fold the beaten egg white into the almond and lemon mixture. Line a springform pan (26 cm Ø) at the bottom with baking paper and grease the rim. Pour in the mixture, smooth it down and bake in a preheated oven, 2nd stage from below (electric oven: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 50 minutes. Cover the cake after approx. 40 minutes and bake it ready. Let the finished cake rest in the switched off oven for another 10 minutes. Let the cake cool down in the mould on a cake rack.
Wash the rest of the lemon hot, dab dry and peel into fine strips. Squeeze the lemon. Sift icing sugar and mix with 3 tbsp lemon juice and 1-2 tbsp hot water to a smooth, thick icing. Pour the lemon icing onto the cake, spread it and sprinkle with lemon zests. Leave to dry for 2-3 hours.