Line baking tray with baking paper. Draw 2 circles (approx. 15 cm Ø) on it. Form four rolls (2 cm Ø) from aluminium foil. Wash the lemon thoroughly, rub dry and rub half of the peel off.
Slightly warm the egg white in a warm water bath. Stir several times. Cream fat, sugar and 1/2 sachet vanilla sugar. Stir in the egg white. Add lemon zest and ground almonds. Sift the flour on top and stir everything in.
Place 1 tablespoon of dough in each circle, spread evenly and sprinkle some flaked almonds on top. Bake in the preheated oven (electric oven: 175 °C/ gas: level 2) for 10-12 minutes until golden brown.
Remove the tray from the oven. Remove the dough sheets from the baking paper immediately and wrap them around the foil rolls while still hot. Let them cool down. Pull out the rolls carefully. In the meantime bake 8 more rolls of remaining dough.
Break the couverture into pieces and melt in a hot water bath. Dip the ends of the rolls into the couverture. Place on a grid and allow to set. Squeeze 1/2 lemon. Whip cream, 2 tablespoons lemon juice and the remaining vanilla sugar until stiff.
Pour into the pastry rolls.