1.Preheat oven to 180°C (160°C fan-forced). Grease 20cm x 30cm lamington pan; line base and two long sides with baking paper, extending paper 2cm above sides.
2.Beat butter, sugar and egg yolk in small bowl with electric mixer until light and fluffy. Stir in sifted combined flours and custard powder. Using fingers, press mixture over base of pan.
3.Bake, uncovered, about 15 minutes or until browned lightly.
4.Meanwhile, make muesli topping. Heat honey and butter in small saucepan until butter melts; transfer to large bowl. Stir in oats, cornflakes, coconut and apricot.
5.Remove slice from oven, spread with jam. Press muesli topping over jam, pressing gently with fingers. Return to oven; bake a further 15 minutes.
6.Cool slice in pan before cutting into 20 pieces to serve.