For the mousse, whisk the yolks and sugar together until pale, thick and doubled in volume. In a pan on a medium heat, gently heat the milk and cream until steam begins to appear. Remove from the heat and – whisking as you go – very gradually pour in the yolk mixture.
Pour back into the pan and cook on a low heat for 6–8 minutes, stirring continuously. Using a sugar thermometer, simmer until it reaches 83ºC and is thick enough to coat the back of a spoon.
Turn off the heat, snap in the chocolate and whisk until smooth. Place a piece of greaseproof paper on the surface of the mousse to prevent a skin forming and leave to cool. Once cold, pop in the fridge.
Preheat the oven to 170ºC/338ºF/gas 3. To make the brownie, snap the chocolate into a heatproof bowl, add the butter, and melt over a pan of gently simmering water until combined. Set aside.
In a separate bowl, whisk the eggs, sugar and salt until fluffy and tripled in volume. Gently fold in the melted chocolate, in batches, followed by the flour. Finally, break up and stir in the amaretti biscuits.
Pour the brownie mixture into a lined 30cm x 15cm tin and bake for 20–25 minutes, or until crisp on the outside but slightly wobbly. Remove from the oven and leave to cool in the tin, then transfer to a wire rack to cool completely.
For the mascarpone cream, place the eggs and sugar in a heatproof bowl over a pan of gently simmering water. Whisk continuously for 8–10 minutes, or until the temperature reaches 82ºC, and the mixture is pale, thick and has a ribbon-like consistency when dropped off the whisk. Allow to cool slightly.
In another bowl, whisk the cream and mascarpone to soft peaks. Fold in the egg mixture, cover and put in the fridge until needed.
When you're ready to assemble the trifle, whisk the dulce de leche to loosen and crumble up the brownie. Layer roughly one third of the brownie in the bottom of a 23cm glass bowl or trifle dish. Drizzle over one third of the amaretto and one third of the mascarpone cream. Spoon over a third of the dulce de leche followed by a third of the chocolate mousse, then repeat the layers twice more.
Finish the trifle with any remaining bits of brownie, and decorate with marshmallows and caramel popcorn, if you like, then serve. Sparkler optional!