1. First, let's make the Duchess cake. Break the biscuits into small pieces (each biscuit into 6-8 small pieces). Place them in a large bowl.
2. In a saucepan, combine the butter, evaporated milk, hazelnut praline, and drinking chocolate powder. Stir until the butter has melted. Allow the mixture to cool slightly. Pour the mixture over the broken biscuits and stir to ensure they are well coated.
3. Let it sit for 5 minutes, then stir again. Repeat this one more time. This will help the biscuits absorb the mixture better and make the Duchess cake more cohesive. Line a 26cm springform pan with plastic wrap, leaving plenty of overhang.
4. Pour the mixture into the pan. Press down with a spoon to spread the Duchess cake evenly. Cover with the overhanging plastic wrap and press down firmly. Refrigerate for 4-5 hours to set and make it easy to unmold.
5. Remove the plastic wrap from the surface and invert the Duchess cake onto a serving platter. Release the springform ring and carefully remove the base of the pan and the plastic wrap. Next, decorate the cake. First, attach the chocolate finger biscuits around the sides, then decorate the top with the colorful chocolate candies.
