Pre-heat the oven to 175°C (350°F). Using 5g of the melted butter, grease a small bundt pan (mine was 1 liter), and then "flour" with cocoa.
Melt butter and stir in the milk and coffee.
In a separate bowl, beat the eggs and sugar until fluffy. Add the butter mixture and continue to whisk until well combined.
Combine the flour, cocoa, baking powder and vanilla sugar and then sift into the wet ingredients, mixing until just combined (being careful not to over mix).
Bake for around 30-35 minutes - the cake is ready when an inserted skewer comes out clean.
Let the cake sit in the tin for around 20 minutes and then remove it and allow it to cool completely on a wire rack.
Melt the chocolate and drizzle over the cake (I let mine run down the tracks created by the bundt tin). Sprinkle with Maltesers, nuts or whatever else you fancy. Enjoy!