Preheat the oven to 180 degrees C. Using a kitchen brush grease and flour very well a large bundt cake pan.
In a bowl combine flour, baking powder, nutmeg and cinnamon.
In a large mixing bowl beat eggs and sugar for 5 minutes. Add vegetable oil and beat for 1-2 minutes until incorporated. Add ground apples, vanilla and milk and stir with a spoon until combined.
Gradually add the dry ingredients, mixing gently with a wooden spoon, until just absorbed.
In a heatproof bowl over a pan of gently simmering water combine chocolate, butter and sugar. Stir until all ingredients are almost melted. Remove the bowl from the heat and whisk vigorously with a spoon until the remaining small pieces of chocolate and butter are completely melted. Add eggs and vanilla and whisk for 2-3 minutes with a hand whisk. Add flour and stir gently until combined.
Pour half of the apple batter into the prepared bundt pan. Spread on top the chocolate batter. Cover with the remaining apple batter.
Bake for 50-60 minutes or until a wooden skewer inserted in the cake comes out clean.
Remove the pan from the oven and let cool for 30 minutes. Carefully run a butter knife around the edges of the cake. Invert the cake on top of a serving plate. Before serving sprinkle with powdered sugar.