For the Croissants:

1. Place the flour, sugar, yeast, and salt in a large bowl and whisk together until combined.
2. Slice the First Choice Butter into 1/2 cm thick squares and toss in the flour mixture to coat. Make sure that the butter remains cold and hard.
3. Add the First Choice milk and stir together until a stiff dough forms. The butter will not be dissolved into the dough completely.
4. Wrap the dough tightly in cling wrap and chill for 1 hour.
5. On a lightly floured surface, roll the dough into a long rectangular shape.
6. Fold it into thirds (like a letter), turn 90 degrees, and repeat 4 to 6 more times, or until the dough has large streaks of butter in it but is smooth and flat. (If at any point the butter starts to feel soft, chill it in the refrigerator or freezer until stiff.)
7. Wrap tightly and chill for 1 more hour, then divide the dough in half and roll each portion out to a thickness of about 1/2 cm, in a long rectangular shape.
8. Cut the dough into long, skinny triangles (about 12 cm at the wide end).
9. Notch the wide end of each triangle with about a 2cm cut, then roll from the wide end to the pointed end, tucking the point under the croissant.
10. Place on a baking paper-lined baking sheet, cover loosely with plastic wrap and allow to sit for 2 hours.
11. Preheat the oven to 180°C and gently brush the croissants with egg wash.
12. Bake for 15 to 20 minutes, or until puffed, golden brown, and flaky.

For the Filling:

1. Heat Custard in a small pot.
2. Mix the cornflour and sugar with 1/2 cup of Custard.
3. Whisk into heated Custard and continue to whisk while the Custard is on medium heat.
4. Remove from heat when Custard thickens.
5. Pour into a piping bag and pipe into the centre of the croissants.
6. Dust lightly with icing sugar.