To make the pastry cream, place milk and vanilla bean in a saucepan. Heat gently until the milk almost boils. Remove from the heat, whisk the yolks, sugar and cornflour in a bowl until thick and pale. Gradually whisk in the warm milk. Return mixture to same saucepan and stir over medium heat until the custard boils. Spread over a tray to cool rapidly. Cover the surface of the custard closely with plastic wrap to prevent a skin forming, at 55°C transfer to a bowl and stir through butter and refrigerate to cool completely
Preheat the oven to 210 degrees celsius convection. Lightly grease 4 oven trays and set aside. Combine the butter with water, sugar, milk & salt in a large heavy-based saucepan and bring to the boil. Remove from the heat and using a wooden spoon quickly beat in the flour. Return to the heat and continue beating until the mixture comes together and leaves the side of the pan. Cook, beating over low heat for 1-2 minutes to cook flour. Remove from heat and allow to cool slightly
Transfer to a large bowl. Using a hand mixer, beat the mixture to release any more heat. Gradually add the eggs, one at a time. Beat well between each addition until all the eggs have been added and the mixture is thick and glossy. Beat for a few more minutes, or until thickened.
Spoon the mixture, in batches, into a piping bag fitted with a 1.25-1.5cm nozzle. Cover remaining pastry with cling film. Pipe mixture onto trays about 3cm x 2cm high leaving room for spreading. Bake for 25-30 minutes, in batches, or until firm and hollow when tapped. Transfer puffs to wire racks.
Put custard into a piping bag with a nozzle less than 1cm. Poke a small hole in the base of each puff and fill with custard.
For the caramel, combine water and sugar in a saucepan until it boils add glucose, and cook until caramel in colour. Remove from the heat and dip the base of the pan in a bowl of water to cool slightly. Grease a cake ring and place ring mould on a baking paper lined tray, pour enough caramel to coat the base 5mm. This is the base for the croquembouche.
Dip the puff bases in enough toffee to coat and place upside down on a tray lined with baking paper.
To assemble, oil the croquembouche cone. Dip the sides of the puff balls in the toffee one at a time and place around the base of the cone. Continue adding balls until the cone is covered.
Transfer the base for the croquembouche to a serving plate. Place a small amount of caramel on the base. Grasp croquembouche gently and lift from the cone and place on the caramel base.
Re-heat the remaining toffee then dip two forks back to back in it. Spin toffee around the Croquembouche. Decorate with violets.