1.Preheat oven to 160°C. Grease 20cm x 30cm (8-inch x 12-inch) rectangular pan and line base and long sides with baking paper, extending paper 5cm (2 inches) over sides.
2.Place biscuits in a single layer over base of pan, trimming to fit if necessary.
3.Combine chocolate and butter in medium saucepan; stir over low heat until smooth. Remove from heat.
4.Beat eggs, egg yolks and sugar in medium bowl with electric mixer until thick and creamy; beat in warm chocolate mixture.
5.Pour mixture over biscuits. Bake about 25 minutes or until filling is set. Cool 15 minutes then refrigerate 1 hour. Dust slice with sifted cocoa before cutting.