Preheat oven to 375°. In a small bowl, combine flour and brown sugar; cut in butter until crumbly. Stir in pecans. Spread in a single layer into a greased 15x10x1-in. baking pan. , Bake 9-12 minutes or until golden brown, stirring once. Cool on a wire rack 10 minutes., In a large bowl, beat ice cream and lemonade until blended. Sprinkle half of the crumbles into a greased 13x9-in. dish. Spread with ice cream mixture; sprinkle with remaining crumbles. Cover and freeze overnight. Remove from the freezer 15 minutes before serving.