lightly grease a 19cmx29cm slice pan & line base with baking paper.combine flour & brown sugar in a food processor, process until well blended, then add butter & process again until mixture resembles breadcrumbs. alternatively, sift flour into large bowl, stir in brown sugar & rub in butter with fingertips. press half the mixture firmly over base of prepared pan. mash 1 large banana to give 1/2 cup mashed banana.