Preheat the oven to 170°C.
Grease a 25cm cake tin and line with greaseproof paper.
Cream the butter and sugar until pale and light.
Mix the sunflower oil and vanilla extract into the beaten eggs.
Gradually beat the egg mixture into the butter and sugar.
Combine the flour, bicarbonate of soda, baking powder, salt, cinnamon, and cocoa powder.
Fold the flour mixture into the cake batter one spoonful at a time.
Carefully stir the flat cola into the batter.
Pour the batter into the tin and level the top.
Bake for 75 to 80 minutes until a skewer comes out clean.
Remove the cake from the tin and cool on a wire rack.
Cut the cooled cake in half horizontally.
Layer the bottom cake with jam and whipped cream then top with the second cake.
Melt the chocolate over a pan of simmering water and spread over the cake.
Decorate with sweets and chocolate buttons while the topping is soft.