First, you need to put your butter or oil in your braiser. And mix until it melt.
Put your milk, cacao and sugar over rhe oil and mix these ingredients until they were quiet smooth.
And finally put your chocolates and mix again.
Your biscuits have to be small enough to have perfect mozaic cake. After 20 mins later, when chocolate souce gets warm enough, put the all souce into the biscuits.
Souce and biscuits have to mix perfectly. And put the mixture on the stretch film. Make a triangle or cylindrical shape with your hands. After that tie the head and end of the film.
It is almost done. Your cake will be ready 2 or 3 hours later in fridge.