Start by making the orange purée, place 2 liters of water into a large pot set over high heat. Bring the water to a boil, once boiling add the whole oranges to the pot. Allow the oranges to boil for 2 hours or until soft. Top up the water if necessary.
Once soft, remove the oranges from the water and chop them into large chunks. Purée the oranges in a food processor until smooth and set the purée aside.
Preheat the oven to 180°C and butter and flour a bundt cake tin.
In a bowl of an electric mixer fitted with a whisk attachment, add the oil, eggs, and sugar. Beat at medium-high speed for about 3 minutes.
Sift the flour and salt together and add this to the egg mixture, beat at medium-low speed until the ingredients have incorporated.
In a jug mix together the milk and the vanilla, in a steady stream with the motor of the electric mixer running, add the milk mixture to the cake batter. Continue mixing until the cake batter is smooth. Scrape down the side of the bowl to ensure the batter is lump-free.
Measure 220 grams of the orange purée and using a spatula fold this through the cake batter. Make sure everything is well mixed. Pour the batter into the prepared cake tin and bake for about 50 minutes or until a skewer inserted into the cake comes out clean.
Once the cake is cooked, allow the cake to cool in the tin for about 20 minutes before tipping it onto a cake plate.
Chocolate Ganache
In a small saucepan set over medium heat, add the chocolate and the cream. Allow the chocolate to melt, stirring occasionally with a spatula. Continue mixing until the chocolate is melted and the ganache is smooth and shiny.