• Pre-heat oven to 180°C.
• Prepare 3 baking trays. Line one with a silicone mat. For the other 2, draw 10cm diameter circular templates on baking paper. Draw 5 circles in total.

For the Hazelnut Praline Paste

• Add hazelnuts to the silicone lined baking tray to lightly roast for 5
• Add sugar to a saucepan over high heat and allow a caramel to form. Move the saucepan in a circular motion to fully combine sugar.
• When all the sugar has melted and the caramel is a deep amber colour, add 135g of hazelnuts to the saucepan and combine with wooden spoon. Reserve remaining hazelnuts for garnishing.
• Spread the caramel-coated hazelnuts over the silicone lined tray. Transfer to the freezer to cool for 10 minutes.
• Once cool and solid, break into shards and add to a high-powered blender. Blend for 5 minutes on high or until a thin paste is achieved. If the praline has not turned to liquid, add vegetable oil,1 tablespoon at a time, blending for 2 minutes after each.
• Transfer 50g of the praline paste to a piping bag and set aside at room temperature. Reserve the remaining paste for the hazelnut mousseline.

For the Pate-a-Choux

• Increase oven to 200°C.
• Combine water, milk and butter in a medium saucepan over a medium heat. When butter has fully melted, remove from heat and add flour, stirring vigorously until fully combined.
• Return saucepan to medium heat and mix until the dough comes away from the edges and forms a ball, around 2 minutes.
• Transfer dough to the bowl of a stand mixer fitting with a paddle attachment. Mix on low speed for 2 minutes or until the dough is no longer hot. Increase stand mixer speed to medium and add eggs one by one, waiting for the dough to recombine before adding the next.
• Transfer the dough to a piping bag fitted with a 12mm round nozzle and place in fridge for 5 minutes. Holding the pastry bag vertically over a lined baking tray, pipe a circle of dough over the drawn template. Repeat to make 5 choux.
• Transfer to the oven and bake for 15 minutes, then reduce oven temperature to 160°C and bake for a further 15 minutes. Do not open the oven door at any point.
• Once cooked, turn the oven off and allow to cool with the door open for 10 minutes. Transfer to a wire rack and allow to cool for another 10 minutes. Set aside for plating.

For the Hazelnut Mousseline

• Add milk and split vanilla beans to a saucepan over medium heat and bright to a light simmer.
• Meanwhile, whisk together sugar, cornflour and egg yolks until pale.
• Discard vanilla beans and add a third of the milk into the egg yolk mixture, whisking constantly while adding. Add the remaining milk, whisking constantly.
• Return the mixture to the same saucepan. Cook over medium heat, whisking until pastry cream begins to thicken, about 5 minutes.
• Once thick, place in a bowl or baking tray with cling wrap pressed over the surface to prevent a skin. Allow to cool in the fridge for 30 minutes.
• Meanwhile, add butter to the bowl of a stand mixer fitted with a whisk attachment and whip until pale and fluffy, about 2 minutes.
• Remove pastry cream from fridge and add a third to the whipped butter. Beat for 10 Add remaining pastry cream and beat for 30 seconds. Add remaining praline paste and fold through the cream mixture until incorporated.
• Transfer mousseline to a piping bag fitted with a 12mm star tip and set aside in fridge for plating.

To Assemble

• Carefully slice the pate-a-choux in half horizontally. Set aside the top.
• Pipe a small amount of praline paste around the choux. Over the praline paste, pipe a generous amount of hazelnut mousseline.
• Return the top of the choux. Pipe 5 dots of praline paste over the top and place a hazelnut halve on each. Dust with icing sugar to finish.