CAKE: Mix all ingredients briefly. Pour into 8x10 inch oiled and buttered baking pan. Bake at 175 C (350 F) for about 40 minutes or until skewer inserted in the middle of the cake comes out clean and the top of the cake is golden brown.
Let cake cool to room temperature. Cut the cake in half. Crumble upper half into a bowl.
SYRUP: While cake is baking, cook water (or orange juice) and sugar until sugar is dissolved. Blend together (using regular blender or handheld blender) with oranges and jam. Pour the mixture over crumbled cake. Stir to combine and transfer into the pan over bottom half of the cake.
CHOCOLATE FROSTING: Put chocolate, sugar and butter in a double boiler and melt. Add the egg (or whipping cream) and mix until it thickens and reaches temperature of 80 C (175 F). Pour over cake.