Peel and core two medium apples, then chop into small cubes.
Transfer the apple cubes into a blender and process until completely smooth.
In a bowl, crack two eggs and add 1 tsp vanilla sugar. Whisk until lightly frothy.
Pour the egg mixture into the blender with the apple purée. Blend briefly to combine.
Add 100 g (¾ cup) of unsweetened cacao powder into the blender. Blend until thick and smooth.
Preheat your oven to 180°C (350°F).
Use a silicone mould or line a small loaf pan with parchment paper.
Pour the chocolate mixture evenly into the mould, smoothing the top with a spatula.
Bake in the preheated oven for 30 minutes.
Let the cake cool in the mould before slicing into pieces. Serve warm or chilled.