1. Add the milk, heavy cream, cocoa powder, butter, and vanilla extract to a small pot. Heat up slowly until the butter has melted and you got a smooth chocolate sauce. Set aside and let cool down a bit.

2. Preheat the oven to 180°C (350°F). Line a 9 inches (20cm) springform tin with baking parchment and grease lightly. Set aside.

3. Add the eggs and sugar to a large bowl and whisk on high for several minutes until very light and fluffy. Mix the flour with baking powder, and salt and sift in several batches into the bowl, and fold in. Gradually add the chocolate sauce and mix/fold in. Pour the batter into the prepared baking tin and bake for 35-40 minutes or until a wooden skewer inserted into the center comes out clean. Take out of the oven and let cool down inside the tin for some time, then remove carefully and let cool down completely on a wire rack.

4. For the buttercream add the milk, cocoa powder, and vanilla extract to a microwave-safe bowl, mix, and heat up until you got a smooth and thick “chocolate milk”. Let cool down completely.

5. Add the butter to a large bowl and whisk on high until very light and fluffy – about 5-6 minutes. Add the cooled chocolate milk and about 2/3 of the confectioners’ sugar to the bowl and mix slowly at first, then on high until well combined. Add more confectioners’ sugar if you like and continue mixing for 3-4 minutes until the buttercream is very creamy and fluffy.

6. Place the cake on a serving plate and spread the buttercream all over the top. Sprinkle with some chocolate shavings or sprinkles.