Melt 200 g of butter and 200 g of dark chocolate together in a double boiler or gently in the microwave, stirring until smooth. Set aside to cool slightly.
In a separate large bowl, beat the 5 eggs and 200 g sugar together until light and fluffy.
Pour in the melted chocolate mixture and stir gently to combine.
Sift in 100 g of flour and fold it into the mixture gradually, making sure not to overmix.
Pour the batter into a greased and floured cake pan (round or square).
Bake for 25–30 minutes. A toothpick inserted in the center should come out clean. Let cool completely before slicing.
2️⃣ Make the Cream Filling:
In a saucepan, whisk together 250 ml milk, 2 tbsp flour, 2 tbsp cornstarch, and 100 g sugar until well combined.
Cook over medium heat, stirring constantly until the mixture thickens to a custard-like consistency (about 5–7 minutes).
Remove from heat and allow to cool slightly. Stir in the 2 egg yolks and 1 packet of vanilla sugar or 1 tsp vanilla extract while still warm, mixing thoroughly.
Once the custard is cool, beat in the 200 g room-temperature butter using a mixer until smooth, creamy, and fluffy.
