To make the rough puff pastry, sift the flour into a large bowl and add the butter. Mix the butter around to coat it in flour (stop before it starts to look like breadcrumbs as you want squashed pieces of butter showing in the mixture). Mix the water and lemon juice together in a jug and pour it into the flour and butter mixture.
Chop the butter into the flour, until the dough comes together. When the dough has formed a loose lump, tip it onto a lightly floured work surface and shape it into a thick rectangle. Roll the dough out, then fold one-third of the dough to the centre, then fold the other third over that. Roll the pastry out again to the same proportions as before and fold in the same way as before. Rotate the pastry a quarter turn and repeat the rolling and folding. Continue for another 3-4 more times. Wrap the pastry in cling film and place into the fridge to chill for several hours.
Preheat the oven to 200C/400F/Gas 6 and lightly grease a baking tray with flavourless oil.
To make the choux pastry, in a large pan bring the butter and 300ml/10fl oz water to boil. Add the flour, remove from the heat and mix well before beating in the eggs one by one. Set aside while you roll the rough puff pastry.
Lightly dust a clean work surface with flour. Remove the pastry from the fridge and roll out until it’s the thickness of a pound coin. Use a 30cm/12in flan ring to cut the pastry to shape. Using a large circular nozzle, pipe some large choux buns around the edge of the puff pastry (approximately 10). On the greased baking tray, pipe out approximately 20 small choux buns. Place the pastry and choux buns into the oven for 25 minutes.
For the crème pâtissière, whisk the egg yolks and sugar together in a bowl until pale and light, then fold in the vanilla seeds and cornflour. Bring the milk to the boil in a small saucepan and then whisk it gradually into the egg mixture. Pour the mixture into a clean pan and bring it slowly to the boil until it thickens. Stir in the butter and simmer for a minute and then remove the pan from the heat.
For the passionfruit curd, in a food processor blend the passionfruit pulp and sieve into a heatproof bowl. If you are using a microwavem, whisk in the whole eggs, egg yolks and sugar. Stir in the butter and place the bowl in a microwave on a medium temperature for two minutes. Whisk, then return to the microwave for two more minutes. Whisk again, then return to the microwave for a final minute. By now the curd should be thick and smooth. If you don’t have a microwave, beat the eggs, egg yolks and sugar together in a bowl. Melt the butter over a low heat in a heavy-based pan and add the egg mixture and blended passionfruit. Cook gently, stirring constantly until thickened. Pour into a shallow bowl, cover with cling film and place in the fridge to cool.
When the puff pastry is cooked, remove from the oven and brush with the egg white. Cook for a further minute then set aside to cool.
For the small choux buns, prick the undersides with the tip of a sharp knife and place back into the oven for five minutes to crisp up. Remove and set aside to cool.
To make the crème Chantilly, whip the cream until thickened using a handheld electric beater and add the vanilla seeds and icing sugar. Place in the fridge in a large mixing bowl.
Spoon the crème Chantilly into a piping bag fitted with the large star nozzle. Pipe into the choux buns by inserting the nozzle into the cut made earlier.
Once the choux buns are filled, make the caramel. In a medium pan set over a high heat, add the sugar and 100ml/3½fl oz water and melt to an amber caramel. Remove from the heat and, using tongs, dip the choux buns into the caramel and place the choux buns into the middle of the gâteau, ensuring some room is left for the cream, chocolate ganache and curd to go on top.
To make the ganache, in a heat proof jug melt the chocolate and cream in a microwave on a low setting. Allow to cool slightly, then pour into the centre of the gâteau. Spread the passionfruit curd over the top.
To decorate, pipe the crème Chantilly in the centre of the gâteau, and into any gaps between the choux buns. Place the strawberries in a ring around the edge of the cream.
To make the spun sugar decorations, in a pan set over a medium heat melt the sugar with two tablespoons of water until a caramel forms (it will be a deep amber colour). Remove from the heat and allow the caramel to cool a little. Line a tray with parchment paper. Using a spoon, carefully drizzle the caramel into shapes on the parchment paper. Take care not to burn yourself as sugar gets very hot. Set aside to cool and harden.
Spike the sugar shapes into the cream in between the choux buns and decorate with a sprinkling of the gold leaf.