01 -
In a food processor, pulse hazelnuts and Maria cookies until crumbs resemble fine, dry sand. Set aside.
02 -
In a large saucepan, combine 1 litre milk with sugar. Heat over medium until sugar dissolves and milk steams, about 5 minutes. Separately, whisk remaining 100 ml milk with cornstarch and egg yolks. Temper yolk mixture with a ladle of the hot milk, whisking constantly. Return tempered yolks to pan and cook, stirring constantly, over medium-low heat until thickened. Remove from heat and divide evenly into two bowls. Cool completely.
03 -
In a food processor, process hazelnuts until smooth and creamy, forming hazelnut butter. Mix hazelnut butter into one bowl of cooled pastry cream. Cover surface with cling film and refrigerate for at least 4 hours or overnight. Just before assembly, gently fold in 1/4 of the whipped cream to create the mousse.
04 -
Add Nutella to the second bowl of cooled pastry cream, mixing thoroughly. Cover with cling film, pressing directly on the surface, and refrigerate for at least 4 hours or overnight. Before assembly, fold in 1/4 of the whipped cream to form Nutella mousse.
05 -
Using a hand mixer, beat heavy cream and confectioner's sugar on medium-high speed until stiff peaks form, about 1 minute. Divide into four portions: one each for the hazelnut mousse and Nutella mousse, and two for layering and topping.
06 -
In a large trifle dish, distribute hazelnut crumbs evenly as the base. Layer the Nutella mousse carefully over the crumbs, keeping layers distinct. Arrange halved Ferrero Rocher chocolates atop the Nutella mousse, placing some cut side against the glass and others flat. Spoon hazelnut mousse evenly over chocolates. Finish with a generous layer of whipped cream and decorate with whole Ferrero Rocher chocolates.