Grease a 28 x 20 cm (11 x 8 inch) shallow rectangular baking tin. Beat together the butter, sugar and syrup until creamy.
Add all the remaining ingredients and beat well until combined. Turn into the tin and level the surface with the back of a dessertspoon.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 35 minutes until deep golden. Leave to cool in the tin.
Turn out on to a wooden board and carefully cut into 16 fingers using a serrated knife.