Makes 30 to 32cm round tart
150g icing sugar
400g plain flour
4 tbsp cocoa powder, good quality
240g unsalted butter, diced and softened
1/2 vanilla pod, seeds only
6 egg yolks
Chocolate hazelnut mousse
2 egg whites
55g caster sugar
185g milk chocolate, melted and cooled
120g hazelnuts, roasted, peeled and chopped
250ml pouring cream
200g dark chocolate, melted
25g liquid glucose
60g unsalted butter, diced
To make pastry, place sugar, flour, cocoa, butter and vanilla in a food processor and blitz on pulse setting until mix resembles breadcrumbs. Add egg yolks and pulse until pastry comes together.
Remove pastry, wrap in cling film and allow to rest in the fridge for at least 2 hours before using. Preheat oven to 180C.
Line bottom of tart tin with baking paper and spray sides with oil. Remove pastry from refrigerator, unwrap and place between two pieces of baking paper. Roll out pastry to 3-5mm thick.
Carefully lift pastry into tart tin and line tin with pastry. Trim excess pastry off around the top by running a rolling pin across the top. Place a piece of baking paper over the pastry, fill with baking beads or rice and blind bake for 8-10 minutes. Remove paper and beads and bake for a further 5-8 minutes.
Remove from oven and allow to cool. In a clean bowl beat egg whites with an electric beaker to soft peak stage. Slowly add sugar and beat until stiff peaks form then fold in chocolate, followed by mascarpone then hazelnuts. Pour mix into tart base, spreading out evenly.
To make chocolate topping, heat cream in saucepan until just about boiling, stir in chocolate and glucose. Once combined whisk in butter until all melted. Allow to cool before pouring over mousse. Pour over to cover whole tart, pop into fridge for an hour or two before serving.