Mix the sugar and cornflour into a bowl and slowly add the eggs. Ensure that this is well mixed, removing any lumps.
Bring the milk to the boil. Once the milk is boiling, pour the milk slowly into the bowl with the egg mixture.
Pour the egg and milk mixture back into the pan and cook on medium heat for a few minutes until the custard becomes thick. Remove from heat and allow to cool. Cover with a plastic wrap and place in the refrigerator until ready to use.
In the meantime, mix the hazelnut praline (or nutella) with the custard using a whisk.
Semi-whip the cream.
Mix the gelatin with the custard.
Fold the custard into the semi-whipped cream.
Cover with plastic wrap until ready to use.
Base crispy layer
In a bowl mix the praline , the melted milk chocolate, then the butter at room temperature, and then add the feuilletine.Spread a thin layer over the tart base and set aside.
Chocolate Hazelnut Thing (adapted from David Chang’s Momofuku Cookbook)
Place all the ingredients in a microwave proof bowl and microwave in 20 second intervals on high until the chocolate has melted.
Add the caramelized hazelnuts until ready to use.
Bring the sugar and water to a boil in a heavy based pan and let the temperature reach 115c (using a candy thermometer)
Add the toasted hazelnuts and take the pan off the heat.
Mix the nuts until the texture changes to become sugary like and bring back the pan on the heat.
Mix carefully until the sugar turns into a golden caramel colour and place on a silpat or baking paper to cool.
To assemble the tart, pipe hazelnut mousse on to the chocolate tart shell and then top with the Chocolate Hazelnut mixture (I used caramel flavored chocolate ganache), and a few caramelized hazelnuts.