Preheat the oven to 190°C. Sift the flour into a bowl. Put the butter, salt and water in a heavy-based pan and bring to the boil over a medium heat. As the water comes to the boil, remove from the heat and dump in the flour in one go. Immediately stir briskly with a wooden spoon until the flour and liquid are evenly combined.

Place the pan back on a lower heat. Beat continuously for a minute until you have a coherent mass that comes away easily from the side. Remove from the heat and leave to cool for about 3 minutes. (If you add the eggs immediately, the mixture may curdle.)

Beat the first 3 eggs into the mixture, one at a time, making sure each egg is completely incorporated before adding the next. The mixture should be smooth and glossy. If it is too stiff, trickle in some of the additional egg yolk, beating well.

Leave to cool to room temperature. Fit a piping bag with an 18mm round nozzle and fill with the choux mixture. On a greased baking tray pipe 9 balls around the size of a walnut. Repeat with a second tray. Press the tops down with a wet finger. Brush the tops with egg wash. Bake for 15 minutes at 190°C, then lower the temperature to 160°C for a further 10 minutes until golden brown and puffy. Remove from the oven and make a small slit in the base of each ball. Turn off the oven. Return to the oven to dry out completely.

To make the custard cream, place the milk and vanilla extract in a medium saucepan and gently heat through. Combine the sugar, flour, eggs and yolk in the bowl of a freestanding electric mixer, and beat well until light and fluffy. Reduce the speed and add the warm milk in a steady stream. Once the milk has been added, return the mixture to the pan and whisk over medium heat until the sauce thickens. Remove from the heat and immediately whisk in the butter and white chocolate. Cool.

To make the toffee, combine the sugar and water in a small pan and bring to the boil. Add the glucose and lower the heat. Cook until the mixture is a warm caramel colour.

When ready to assemble, pipe a little custard cream through the base slit of each choux ball. Carefully dip each ball into the hot toffee and allow to set on a silicone sheet. Garnish while still sticky with a small fondant flower or butterfly.