1. Preheat the oven to 180°C (350°F) on the fan setting. Grease and flour a round cake pan with a hole in the middle. In a bowl, sift the flour, cornstarch, baking powder, and vanilla, and mix them together.
2. Add the salt. Mix and set aside. In a small bowl, mix the cocoa with the hot water. In another bowl, mix the vinegar with the soy drink. Set this aside for 5 minutes. In a bowl, combine the sugar and the orange zest. Rub them together to release the orange essential oils.
3. Add the sunflower oil to the sugar and zest mixture and beat very well. Put the baking soda into the orange juice and stir. Be careful, this step should be done over the mixing bowl because the soda foams up quickly. Add this to the bowl and mix.
4. Pour in the soy drink mixture with the vinegar, mix, and gradually add the flour mixture. Mix well and divide the batter into 2 bowls. In one bowl, mix in the cocoa mixture. Pour half of the plain batter into the pan and then spoon about 2/3 of the cocoa batter over it.
5. Pour the remaining plain batter on top, and then drizzle the rest of the cocoa batter over the center of the cake. Use a wooden skewer to create patterns on your cake. Bake in the preheated oven for 45 minutes. To check if it's done, insert a wooden skewer into the center of the cake; if it comes out clean, it's ready.
