Preheat the Oven: Preheat your oven to 180°C (350°F). Grease and flour a cake pan with a diameter of 18x27 cm.

Mix the Wet Ingredients: In a bowl, beat the eggs with a pinch of salt, vanilla sugar, and 100g sugar until light and fluffy. Add the oil and milk, mixing well.

Combine Dry Ingredients: In a separate bowl, sift together the flour and baking powder. Gradually add the dry ingredients to the wet mixture, stirring until well combined.

Bake the Cake: Pour the batter into the prepared cake pan and bake for approximately 30 minutes or until a toothpick inserted into the center comes out clean. Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Mix Cocoa and Coffee: In a small saucepan, combine bitter cocoa, sugar, instant coffee, and milk. Cook over medium heat, stirring constantly, until the mixture comes to a gentle boil.

Melt Chocolate: Add dark chocolate and butter to the saucepan, stirring until melted and smooth.

Thicken the Filling: Mix a little water with cornstarch to create a slurry. Add the slurry to the chocolate mixture, stirring constantly until it thickens. Reserve half of the mixture and let it cool in the refrigerator.

Layer the Cake: Once the cake has cooled, slice it horizontally to create two layers. Spread half of the chocolate filling evenly between the layers and over the top of the cake.

Decorate: Sprinkle chocolate vermicelli over the top of the cake for a decorative touch.