Peel and core the apples. Dice one apple and slice the other one. Put the diced and sliced apples into two different bowls and season them with the lemon juice.
To a large bowl, add the dry ingredients: the flour, the sugar, the cinnamon, the diced apple (keep out the lemon juice) and mix well. Set aside.
To a small bowl add : the soy yogurt, the sunflower oil, the baking powder and the lemon zest. Mix well. Add this ingredients to the dry ingredients and stir until just combined in a soft batter.
Pour the batter into a greased and floured plum cake pan and arrange the sliced apple (keep out the lemon juice) on the surface.
Sprinkle the top of the plum cake with some bitter cocoa.
Bake in a preheated oven on 180°C for 40-45 minutes. Set aside to cool down.
Notes
As an alternative to soy yogurt, any vegetable drink (120 ml) can be used, although in my opinion the plum cake remains dry and softer with yogurt.