For the base, chop the chocolate coating and melt in a hot water bath. Squeeze lemon. Mix flour, starch and baking powder. Add butter, sugar, lemon juice and eggs. Mix to a smooth dough with the whisks of the mixer.
Grease the bottom of a springform pan (26 cm Ø) and dust with flour. Quarter the dough and put 1⁄4 into the form. Spread evenly on the bottom. Bake in a preheated oven (electric cooker: 250 °C/circulating air: 225 °C/gas: see manufacturer) for 6-7 minutes.
Carefully remove the base from the mould and place on a cake rack. Immediately spread thickly with liquid chocolate coating. Allow to dry.
Clean the springform pan, grease again and dust with flour. Prepare 3 more cakes in the same way with the remaining dough and chocolate coating. Spread the remaining liquid chocolate coating on the back of a baking tray and let it dry.
For the filling, soak gelatine in cold water. Wash 1 orange hot, rub dry and peel in fine strips. Fillet 2 oranges, collect the juice and squeeze the peel.
Drain the fillets on kitchen paper. Squeeze lemons and other oranges. Mix 75 ml lemon juice and 1⁄4 l orange juice. Heat 3 tbsp. juice. Squeeze gelatine and dissolve in it. Add to the remaining juice with sugar.
Chill for about 30 minutes until the juice begins to gel. Whip cream until stiff and fold in 2 portions.
Place 1 base on a cake plate and spread with 1⁄4 of orange cream. Spread all the cakes one after the other and place on top of each other. Chill the cake for at least 4 hours.
Scrape off the chocolate coating with a spatula. Decorate the cake with orange filets, zest and rolls. Dust with cocoa.