In the bowl of a stand mixer fitted with a whisk attachment, beat the egg whites, gradually adding the caster sugar, until a thick, fluffy meringue forms.
6 large egg, ⅔ cup caster sugar
In a separate bowl, lightly beat the egg yolks with the vanilla extract and salt.
2 teaspoon vanilla extract, pinch of fine salt
Gently fold the egg yolk mixture into the whipped egg whites.
Sift the flour and cornstarch into the mixture. Gently fold with a large metal spoon or silicone spatula until just combined, being careful not to deflate the batter.
¾ cup all-purpose flour, 4 tablespoon cornstarch
Transfer the batter to a piping bag fitted with a large round tip.
Line a baking sheet with parchment paper or a silicone baking mat. Pipe the batter into strips approximately one inch (two and a half centimeters) wide and three inches (seven and a half centimeters) long, leaving space between each biscuit. Use additional baking sheets as needed.
Dust the piped biscuits with powdered sugar. Let them rest for five minutes, then dust again to create the signature crisp crust.
powdered sugar
Preheat the oven to 350°F (180°C). Bake for ten minutes, rotate the baking sheet, and continue baking for another five minutes.
Turn off the oven and leave the biscuits inside to cool and dry overnight.