1.Grease 20cm x 30cm (8-inch x 12-inch) rectangular pan, line base and long sides with baking paper, extending paper 5cm (2 inches) over sides.
2.Process 200g (6½ ounces) of the biscuits until fine, chop remaining biscuits coarsely.
3.Reserve 40 whole choc-malt balls, coarsely chop 1 cup of the remaining balls.
4.Stir butter and condensed milk in small saucepan over low heat until smooth.
5.Combine processed and chopped biscuits with chopped choc-malt balls in medium bowl, stir in butter mixture. Press mixture into pan. Refrigerate 30 minutes.
6.Stir chocolate and oil in medium heatproof bowl over medium saucepan of simmering water until smooth, spread over biscuit base. Top with reserved choc-malt balls. Refrigerate about 1 hour or until set before cutting.
Use un-iced, unfilled plain biscuits for this recipe.Note