Place the softened butter in a bowl and add the icing sugar and cocoa powder along with vanilla extract (if using)
Mix thoroughly until you get a soft mixture like frosting
Heat the milk and add the coffee powder
Mix well to combine
Take your first Marie biscuit and dip into the hot milk for 5 seconds
Remove and place on a plate
Take about 1 tsp of the chocolate frosting and smear over the Marie biscuit
Take the second biscuit and repeat the same process until you have a long biscuit stack with chocolate frosting in between
Smear the remaining chocolate frosting all over the biscuit tower generously
Refrigerate this biscuit tower for approximately 2 hours or overnight
Take it out and lay down on a cutting board
Use a fork to create lines over the chocolate log to resemble the lines on a wooden log
Cut slightly diagonally to get your log cookies, the biscuits would be soft by then
Serve immediately or keep chilled until ready to serve