Cream fat and add lemon peel. Add sugar and eggs bit by bit. Mix flour, cornstarch and baking powder and stir in. Chop the chocolate and fold in.
Line a box mould (30 cm long) with parchment paper. Fill in the dough and smooth it down. Bake in a preheated oven (electric: 175 °C/ gas: level 2) for about 1 1/2 hours. After 15 minutes cut in 1 cm deep.
Leave to rest in the mould for 10 minutes. Remove from the mould and let it cool down. Melt the chocolate coating in a hot water bath and let it cool down. Melt again. Warm up the jam briefly. Cut the cake twice horizontally and fill with jam.
Pour the chocolate coating evenly over the cake. Allow to dry briefly. Decorate with orange slices and nuts. Makes about 16 pieces.