1. Rub the butter into the flour until it starts to bind together. Pat out into a shallow base-lined 30.5 x 1 8 cm (11 x 7 inch) tin.
2. Dredge liberally with the sugar combined with caraway and coriander seeds.
3. Leave overnight in a cool place, then bake in the oven at 180°C (350°F) mark 4 for about 20 minutes.
4. Cut into fingers and cool in the tin. Leave for a day before eating.