Craquelin

1. Combine brown sugar, flour and butter in a mixing bowl 
2. Rub the butter into the flour and sugar using your fingertips
3. Place between two pieces of parchment paper and use a rolling pin to roll it out to 4mm in thickness
4. Freeze
5. Cut into 4cm or 1 1/2" inch round discs with a cookie cutter and reserve in the freezer until ready for use

Choux Pastry

1. Preheat the oven to 230°C
2. Heat milk, water, butter, salt and sugar in a medium saucepan over medium low heat
3. When it starts to boil remove from heat and add the flour in one go, mixing vigorously until smooth
4. Return to heat and flatten the dough to the bottom of the pan, listening for crackling of the dough without mixing
5. Give the pan a shake and when you notice a thin film on the bottom of the pan the dough is sufficiently dry
6. Remove from heat
7. Using a wooden spoon/spatula beat the dough to let steam evaporate and then cool for 10 minutes
8. Slowly add the beaten egg and stir until the dough is smooth, but still holds structure (the batter will form a 'V' or a 'beak' on the spoon/spatula when lifted)
9. Pipe small 3.5cm or 1 1/3" round mounds on a lined baking tray
10. Top with a disc of frozen craquelin
11. Turn down the oven temperature to 160°C and bake for 25 minutes, or until golden brown
12. Remove from oven and poke a hole in the bottom of each puff to release steam
13. Cool on a wire rack

Creme Patissiere

1. Heat milk until just boiling in a small saucepan
2. Meanwhile, in a medium sized mixing bowl combine egg yolks and sugar, whisking until doubled in volume
3. Add the cornflour and mix until combined
4. Pour the hot milk into the egg mixture and whisk until smooth
5. Return the mixture to heat and whisk constantly until thick
6. Remove from heat and add butter
7. Pour into a bowl and cover with plastic wrap, ensuring it touches the surface of the pastry cream
8. Cool in fridge until use

Diplomat cream

1. Whisk the cream until medium stiff peaks are reached
2. Add the cooled creme patissiere and whisk until stiff peaks are reached
3. Transfer to a piping bag with a star tip
4. Reserve in fridge until use

Assembly

1. Using a sharp knife, cut the tops of the choux puffs off
2. Fill with diplomat cream and top with a swirl
3. Place the top of the choux puff on top of the swirl and sprinkle a little icing sugar
4. Repeat until all puffs are filled
5. Store in an airtight container in the fridge and consume within 2 days of filling