Stick to either metric or imperial measures to ensure success.
250g (8 oz) butter, softened
125g (4oz) caster sugar (superfine granulated sugar)
50g (2 oz) cornflour (US cornstarch)
275g (10 oz) standard flour
Pinch of salt
Caster sugar (superfine granulated sugar) for sprinkling
1 Put butter in a bowl and beat until soft and loose. It is easier to do this with a hand-held beater or with a cake mixer. Beat in sugar a tablespoon at a time and beat until creamed (fluffy in texture and pale in colour). Sift cornflour and salt together and blend in, then blend in flour in three lots, sifting it into the bowl.
2 Press dough into a shallow ovenproof tin (approximately 30cm x 20cm/8” x 12”) lined with baking (parchment) paper. Chill for 1 hour.
3 Preheat oven to 120°C (250°F). Bake shortbread for about 30 minutes, or until a pale golden colour and firm. Remove from oven, prick the top with the tines of a fork, sprinkle with caster sugar and mark into bars. Cool in the tin then transfer to a cooling rack. Store airtight.
Standard flour in the UK is milled a little finer than in New Zealand and the dough may need a tablespoon or so more flour. If the dough is sticky when pressing it into the tin, work with floured fingers, or chill the dough for 10 minutes then try.