Place egg whites in a small bowl; let stand at room temperature 30 minutes., Preheat oven to 325°. In a large bowl, cream butter, 1/2 cup brown sugar and sugar until light and fluffy. Beat in egg yolks, milk and vanilla. In another bowl, whisk flour, baking powder, baking soda and salt; gradually beat into creamed mixture. Press into a greased 15x10x1-in. baking pan., With clean beaters, beat egg whites on medium speed until foamy. Gradually add remaining brown sugar, 1 tablespoon at a time, beating on high after each addition until brown sugar is dissolved. Continue beating until thick and glossy. Stir in chocolate chips and pecans. Spread over dough in pan., Bake on a lower oven rack until meringue is lightly browned, 25-30 minutes. Cool completely in pan on a wire rack. Using a serrated knife, cut into bars. Store in an airtight container.