Preheat the oven at 180 C for 10 minutes. Grease a bundt pan very well. Shift plain flour, baking powder and salt together. Whisk eggs, sugar, oil ,melted butter and milk until well incorporated. Add in the extract and stir in the sifted flour.
Divide the mix equally into two separate bowl. Add in zest ,juice and colour to one bowl. Add cocoa mix to another.
Pour few tablespoons of chocolate batter into the bundt pan. Gently shake the pan to evenly spread it out. Now pour the entire mix of Orange batter to the pan. Top it with the remaining batter of chocolate mix.
Bake for 30 to 40 minutes or until done. Remove from oven and let it cool down for 10 minutes. Run a knife around the edges of the pan and slowly remove the cake by turning it upside down with a plate covered.
To make the chocolate sauce. Melt 200g of dark chocolate ( I used plaistowe ) in the microwave in short bursts. Keep checking in between otherwise chocolate gets burned quickly. Now add 300 ml of thickened cream. Stir the mix and microwave it for few more seconds until you get to a pouring consistency. Drizzle this syrup on the cake and serve.