Step 1

Line a 18cm x 28cm slice tin with baking paper. Process almonds in a food processor until finely ground, then transfer to a bowl with flour, icing sugar, baking powder and 1 tsp fine salt. Add butter and rub in with your fingertips to form fine crumbs. Add egg, yolks and half the rind and mix to combine without overworking the dough. Transfer dough to slice tin, pressing evenly over tray, then cover with a piece of baking paper and rub pastry evenly into the corners using a small bottle, side of a cup, or small wooden dowel, then refrigerate to rest (30-40 minutes).

Step 2

Preheat oven to 180C and bake shortbread, turning pan occasionally during cooking, until golden (40-50 minutes). Remove from oven and cool for 10 minutes then, using a 6cm round cutter, cut shortbread in rows in the tin, starting with a round, then overlapping by about half each time to form crescents, removing each as you go. Set aside to cool.

Step 3

Meanwhile, combine remaining rind with icing sugar in a bowl and mix, and sieve mixture heavily over biscuits and serve. Biscuits will keep in an airtight container for up to 3 days.