The cake we used for this roulade can be found here.

It worked fine, but in principle, you can use any chocolate cake for the recipe.

Crumble the cake into a bowl.

Add milk and melted dark chocolate to the bowl with the crumbled cake.

Mix well until you have a soft and uniform mass.

Place a piece of plastic wrap on the table. The length should be about the same as you want your roulade to be.

Place the chocolate mixture on the wrap.

Take another piece of wrap of the same size and place it over the chocolate mixture.

Roll out the mixture with a rolling pin so that it covers the entire surface between the two pieces of wrap.

Combine soft butter, vanilla sugar, powdered sugar, and milk in a bowl.

Whip the ingredients together with an electric mixer until you have a fluffy and smooth buttercream.

Remove the top piece of plastic wrap from the chocolate mixture.

Place the buttercream in dollops and then spread it evenly over the "chocolate base."

Using the bottom piece of plastic wrap, roll the cake together into a roulade.

Wrap the roulade tightly with the plastic wrap so it holds together while it rests in the fridge.

Place the roulade in the fridge for about an hour until it is cold.

Melt the chocolate for the coating.

Place the cold roulade on a rack and pour the chocolate over it so that the whole cake is covered in chocolate.

Return the roulade to the fridge and let it chill until the chocolate has solidified.

Sift a thin layer of powdered sugar over the roulade.

Serve the cake sliced into thin pieces.