Vanilla and Hazelnut Tart

Toast the hazelnuts in the oven for 10 minutes at 150°C / 300°F. When the hazelnuts are warm or cool, rub them between your hands to remove the skins (a little remaining skin is fine).

Bring the water and sugar to a boil. At 118°C / 244°F, remove from the heat and pour the hazelnuts into the syrup. Stir until the mixture turns white and sandy. Return to a medium heat and stir until the sugar melts again and caramelises (this may take a little time).

Spread on baking paper and leave to cool.

Add the fleur de sel and blend in a food processor until you reach a praline consistency.

Store in an airtight jar.

Place the softened butter and icing sugar in the bowl of a stand mixer fitted with the paddle attachment and mix on low speed. Add the ground almonds, vanilla powder and fleur de sel and mix again.

Add the beaten egg and mix using a spatula this time ( it will be easier than with the mixer ).

Finish with the flour and mix using the mixer until you obtain a smooth ball of dough. Do not overwork the dough. Bring it together into a ball without over-handling.

Divide the dough into two and wrap each portion in plastic wrap, shaping them into flat rectangles. Refrigerate one overnight (you can freeze the other for a future tart).

The following day, roll the dough out to 2-3 mm thick with a rolling pin then cut out a circle larger than your tart ring.

Grease the tart ring then lay the pastry in, taking care to create a right angle.

Refrigerate for at least 6 hours (overnight is ideal).

Rehydrate the gelatine in the water.

Break the white chocolate into pieces in a bowl (you can melt it slightly in a double boiler or in the microwave).

Heat the 100 g (3.5 oz) of cream with the halved and scraped vanilla pod in a saucepan and bring to a boil. Cover and leave to infuse for 15 minutes.

Remove the vanilla pod then reheat the cream.

Off the heat, add the rehydrated gelatine and mix.

Pour one third of the cream over the white chocolate and stir with a spatula to create an emulsion. Then pour in a second third, then a third, until the mixture is perfectly smooth.

Add the 200 g (7.1 oz) of very cold cream and mix again. Blend for a few seconds with an immersion blender to thoroughly emulsify everything.

Cover with plastic wrap directly on the surface and refrigerate overnight.

Soak the gelatine leaves in very cold water.

In a bowl, whisk together the egg yolks and sugar until the mixture turns pale.

Add the cornstarch and mix.

Bring the milk to a boil with the vanilla seeds and pod in a large saucepan. Pour three quarters of the milk into the bowl in a thin stream, whisking constantly, then return everything to the saucepan containing the remaining hot milk.

Whisk over a medium heat until the cream thickens, for about 2 minutes.

Add the rehydrated gelatine and mix.

Transfer to a wide dish, cover with plastic wrap directly on the surface and refrigerate overnight.

Preheat the oven to 160°C / 325°F, fan-assisted.

Melt the butter then add the vanilla seeds and leave to cool.

In a blender, blend the almond paste with the eggs until smooth and homogeneous.

Pour this mixture into the bowl of a stand mixer while sieving it (a few small pieces of almond paste may remain). Whisk for 10 minutes to aerate it.

Add the melted butter and oil then the sifted flour and baking powder mixture. Fold in gently with a spatula.

Pour this batter into a greased 22 cm (8.7 in) ring and bake for approximately 20 minutes.

Once cooled, trim the sponge with an 18 cm (7.1 in) diameter ring.

The next day, remove the crème pâtissière from the refrigerator and work it with a whisk until smooth (you can whisk it in the mixer at full speed for one minute).

Add the hazelnut praline and whisk again.

Whip the heavy cream to soft peaks and fold it into the crème pâtissière with a spatula.

Transfer the crème diplomate to a piping bag without a tip. Set aside in the refrigerator.

Preheat the oven to 160°C / 325°F.

Once the pastry is well chilled, trim any excess pastry with a small knife.

Place a sheet of baking paper over the tart shell and top with baking beans or dried pulses to blind bake ( normally, if the tart shell has rested overnight in the fridge, baking beans are not necessary as the pastry will not shrink ).

Bake for 20 minutes then remove the tart from the oven, remove the ring and leave to cool slightly.

Smooth any imperfections in the pastry with a microplane grater if needed.

Brush the base and edges (inside and out) with a mixture of egg yolk and heavy cream to give it a shine (the cream represents approximately 10% of the weight of the yolk).

Continue baking for 10 to 15 minutes (the pastry should be nicely golden). Leave to cool on a wire rack.

Spread hazelnut praline over the entire base of the tart shell then place the pain de gênes sponge in the centre and press down gently.

Pipe the crème diplomate all around the edges first, then over the sponge. It should come up to the rim of the tart. Smooth with a large offset spatula then place in the freezer for approximately 30 minutes to allow the cream to firm up.

Whip the vanilla ganache with a mixer until still supple. Transfer to a piping bag fitted with a P125 tip.

Pipe the whipped ganache delicately starting from the outside, leaving a little space in the centre for the hazelnut praline.

Add a few hazelnuts cut in half and refrigerate until ready to serve. If the sponge is a little too thick and/or you tend towards the indulgent side, you can pipe more crème diplomate to form a small dome. Personally, I would not have said no to a little more cream (you can see from the cross-section photo that there is not a great deal of crème diplomate).