Chocolate shortbread

Grease and line base and sides of a 18cm x 28cm lamington pan. Beat butter 300g unsalted butter and sugar 1 cup (220g) caster sugar in a bowl with electric beaters until pale. Sift in flour 2 1/2 cups (375g) plain flour , cocoa 5 tbsp good-quality cocoa powder and soda 1/4 tsp bicarbonate of soda and beat slowly until just combined. Spread in pan and smooth with a spatula. Prick all over with a fork. Chill for 15 minutes.

Preheat oven to 180°C. Cook shortbread for 25 minutes or until firm to touch. While it's still hot, use a knife to score it into 12 rectangles. Cool slightly, then remove from pan and cut into 12 pieces. Dust with icing sugar Icing sugar, to dust before serving. Shortbread will keep for 3-4 days in an airtight container.