Preheat your oven to 175°C. Melt the chocolate in a bain marie. Whip butter and sugar in a mixer until it is white and fluffy. Stir in melted chocolate and vanilla sugar (vanilla essence) until you have an even mixture. Blend in the egg yolks, one by one. Add orange zest. Sift in the flour, and fold gently into the mixture. In a separate bowl, whisk the egg whites until they form stiff peaks. Stir in about 4 spoonfuls of the egg whites, then carefully fold in the rest. Make sure you do not stir the egg whites in, as it is the air in the meringue that will rise the cake (there is no baking powder)! Pour into a greased 22cm diameter round cake pan with a loose base. Bake on the bottom rack for 40 minutes. Cool on a rack.
Melt the chocolate in a bain marie. Mix in icing sugar and egg white until the mixture is smooth. Do not use a high-speed electric mixer.
Bring double cream gently to the boil while stirring. Pull off the heat as soon as you see bubbles. Add chocolate in pieces, and stir until the chocolate has dissolved entirely.
Unsweetened whipped cream
ASSEMBLY OF CAKE:
Once the cake has cooled completely, cut it in half evenly with a sharp knife. Place the halves side by side with the cut end up. Using a tablespoon, spread blood orange syrup evenly onto the bases and let it sit for about 5 minutes. Once the bases are moistened by the syrup, spread two thirds of the marmalade evenly onto both bases. Continue by spreading chocolate icing on the bottom layer, then place the top layer over. Spread the rest of the marmalade over the top of the cake, and follow with chocolate icing. Use a spatula to even out the icing. Pour the warm ganache over the top of the cake, and let it cover the sides as well as the top. Place the cake in the fridge to set, before drizzling cocoa powder over top and placing the twisted oranges in a decorative pattern.
Leave the cake in the fridge to set (about 15 – 20 minutes) and cut with a warm knife. Serve with unsweetened whipped cream, a drizzle of Blood Orange and Grand Marnier syrup, and a good cup of coffee.