Place the dessert mix contents in a large bowl. Add the salt, milk and hazelnut liqueur and make the chocolate dessert mix according to package instructions.
Mix the milk and hazelnut liqueur together in a bowl to make the soaking liquid. Soak the pieces of ladyfingers in the milk (for about 3 - 5 seconds), and arrange them in one layer on the bottom of a trifle glass.
Pipe or spoon in a layer of the chocolate mousse, followed by some chopped hazelnuts. Repeat these layers once more (soaked ladyfingers, chocolate mousse) and then sprinkle the hazelnut praline on top (instead of chopped hazelnuts). Repeat for 3 more trifle glasses.
Sprinkle the sugar on to the bottom of a clean pan. Heat the sugar over medium heat. Watch the sugar closely as it melts and starts to caramelize. Shake the pan to evenly distribute the sugar as it caramelizes.
Using a spatula, scrape the caramel and hazelnuts onto a silicon pastry mat or parchment paper. Be careful as the sugar will be extremely hot at this point.
Once the praline has cooled and hardened, place the praline in a plastic sandwich bag and crush using a mallet or a stone pestle.