For the semi finals of the Great British Bake off, Paul and Mary set the semifinalist a technical challenge based upon the German baumkuchen cake, the schichttorte.

Traditionally, Baumkuchen is made on a spit by brushing on even layers of batter and then rotating the spit around a heat source. Each layer is allowed to brown before a new layer of batter is poured. When the cake is removed and sliced, each layer is divided from the next by a golden line, resembling the growth rings on a crosscut tree.

Although the German schichttorte cake recipe is considered a simpler bake, it proved to be a tough multi-layer challenge for the remaining bakers. It is traditionally cooked in stages under the grill to create 20 layers of different-coloured sponge.

Typical ingredients includes eggs, caster sugar, plain flour, Amaretto, cocoa powder, dark chocolate, golden syrup and vanilla. But any mistakes or deviation from the recipe could cost the bakers a place in the final.

Paul Hollywood used these ingredients in his recipe:

For the cake: 10 large free-range eggs, separated, 100g unsalted butter, 150g caster sugar, 1 large lemon, zest only, 1 tsp vanilla bean paste, 150g plain flour, sifted, 65g cornflour, sifted, oil, for greasing and 6 tbsp apricot jam.

For the chocolate glaze: 50g unsalted butter, 1 tbsp golden syrup, 1 tbsp rum, 1 tsp vanilla bean paste, 75g plain chocolate (36% cocoa solids), finely chopped, For the vanilla glaze, 250g icing sugar, 1 tbsp rum, ½ tsp vanilla bean paste and 1-2 tbsp milk.