Step 1

Combine the hazelnuts and Maria cookies in the jar of a food processor. Pulse until crumbly and resembling dry sand. Reserve.

Step 2

Combine 4 cups of milk and the sugar in a large saucepan. Cook, over medium heat, until the sugar has dissolved and the milk begins to steam, about 5 minutes.

Step 3

While the milk is on the stove, whisk the remaining milk with the cornstarch and the yolks. When the milk is hot, add a ladleful to the yolk mixture, whisking constantly, to temper.

Step 4

Return the tempered yolks to the saucepan and cook, over medium low heat, stirring constantly, until thickened.

Step 5

Remove from the stove and divide in two bowls. Reserve to cool.

Step 6

Start by making hazelnut butter in a food processor. Just add the hazelnuts and pulse, stopping every now and then to scrape down the sides with a spatula, until smooth and creamy.

Step 7

Once the pastry cream has cooled, mix the hazelnut butter in one of the pastry cream bowls. Cover with plastic, making sure the plastic touches the cream to prevent it from hardening, and refrigerate overnight (or for at least 4 hours).

Step 8

Before assembling, carefully fold 1/4 of the whipped cream into the hazelnut cream, creating a mousse.

Step 9

When the pastry cream is cool, mix the Nutella in one of the bowls. Cover with plastic, making sure the plastic touches the cream to prevent it from hardening, and refrigerate overnight (or for at least 4 hours).

Step 10

Before assembling, carefully fold 1/4 of the whipped cream into the Nutella cream, creating a mousse.

Step 11

Using a hand mixer, beat the heavy cream and sugar at medium or high speed, until stiff peaks form, about 1 minute.

Step 12

Divide into 4 parts - one for the hazelnut mousse, one for the Nutella mousse and the remaining to top the trifle. Reserve.

Step 13

Spread the hazelnut crumbs evenly along the bottom of a large trifle glass dish.

Step 14

Add the Nutella mousse, being careful not to mix the two layers together.

Step 15

Add halved Ferrero Rocher chocolates. You can add some cut side against the glass and others upside down on top of the Nutella mousse.

Step 16

Carefully add the Hazelnut Mousse on top of the halved chocolates.

Step 17

Finish with whipped cream and decorate with Ferrero Rocher chocolates.