Crush cereal to 250 ml (1 cup). Combine with brown sugar and 75 mL (1/3 cup) butter, mixing well. Reserve 50 ml (1/4 cup) crumbs. Press remainder evenly into bottom of 20 cm (8-inch) springform pan ( or 23 cm (9-inch) pie plate ) to form crust. Bake at 180 degrees C (350 degrees F) 7 minutes or until lightly browned. Cool.
Prepare dessert mix according to package directions, except reduce boiling water to 425 ml (1 3/4 cups). Cool 3 minutes, stirring twice. Meanwhile, beat egg whites until soft peaks form; gradually add sugar, beating until peaks are stiff but not dry.
Pour half of the filling onto crust. Gently fold remainder into egg whites. Spread over first layer; sprinkle with reserved crumbs. Chill about 3 hours. Refrigerate leftovers.