The sweet, crunchy topping for these light choux puffs is a frozen mixture of brown sugar, butter and flour. After baking, the buns are filled with a light crème pâtissière with a hint of orange.
Make the craquelin. Put the sugar, flour and soft butter into a bowl and mix well, then bring the mixture together with your hands to make a soft, slightly sticky dough.
Form the dough into a thick disc and place between 2 sheets of baking paper. Roll out to 3mm thick, then place the dough (still in the paper) flat in the freezer while you make the choux pastry.
For the choux pastry, heat the oven to 230°C/210°C fan/450°F/Gas 8.
Sift the flour into a bowl. Put the butter, milk, salt, sugar and 100ml of water into a medium pan and set over a low heat until the butter has melted, then turn up the heat so the mixture comes to boil.
Quickly remove the pan from the heat and add all the sifted flour. Rapidly beat the mixture to make a smooth, glossy dough.
Place the pan back over a low heat and beat more gently for 1 minute, until the dough is very thick and forms a ball.
Tip the ball into the bowl of a stand mixer and leave until barely warm. Then beat in the eggs, a little at a time, beating well after each addition, to make a very smooth, glossy dough that holds its shape.
Transfer the dough to a large piping bag fitted with a 1.5cm plain nozzle and pipe 20 4cm-diameter mounds on the lined baking sheet, setting them well apart. Lightly brush the top of each mound with beaten egg yolk to flatten.
Remove the craquelin from the freezer, peel off the top sheet of paper and use the 3cm cutter to stamp out 20 discs. Place a disc on top of each choux mound.
Put the baking sheet into the oven. Immediately reduce the heat to 190°C/170°C fan/375°F/Gas 5 and bake for about 35 minutes, rotating the sheets after 20 minutes, until the buns are puffed, crisp and golden brown.
Transfer the buns to a wire rack and make a small hole in the side of each with the tip of a small knife or a metal skewer, to release the steam. Leave to cool.
Make the crème pâtissière. Pour the milk into a medium pan, add the grated orange zest and set over a low heat.
Put the egg yolks, sugar and cornflour into a heatproof bowl and hand-whisk for a couple of minutes, until very smooth and light. When the milk is steaming hot, pour it slowly into the bowl, whisking continuously, until combined.
Tip the mixture back into the pan and set over a medium heat. Whisk continuously, until the mixture boils and thickens to make a very smooth, thick custard.
Remove the pan from the heat and whisk in the butter followed by the orange blossom water or liqueur, to taste. Cover the surface with cling film to prevent a skin forming, leave to cool, then chill until ready to assemble.
To fill the buns, uncover the crème pâtissière and hand-whisk so that it’s very smooth and light. Transfer to a large piping bag fitted with a 7mm plain nozzle and pipe the filling into each choux bun through the steam hole. Serve as soon as possible.