Step 1

Process flours, sugar and a pinch of salt in a food processor to combine, add butter and half the orange rind and process until fine crumbs form, turn onto a work surface and bring together with the heel of your hand. Knead in glacé orange, then roll out on a piece of baking paper to a rough 21cm-diameter round. Trim edges, using a 20cm-diameter plate as a template, then transfer to an oven tray, using baking paper to assist. Pinch with your fingers to form a scalloped edge and refrigerate until firm (30 minutes).

Step 2

Preheat oven to 150C. Brush dough with eggwhite. Combine white sugar and remaining orange rind in a small bowl, scatter over dough, then score halfway through dough to form 12 wedges. Prick dough with a fork, piercing all the way through. Bake until light golden (40-45 minutes), cool slightly, then cut through score marks into pieces and cool completely. Store in a single layer in an airtight container until required. Shortbread will keep for 1 week.