Heat oven to 350. Put flour, baking powder & salt into ungreased 8" square pan. Stir with fork to mix well. Stir in prunes & orange peel. Add milk, oil, peanut butter & eggs. Stir until blended. With rubber spatula, scrape any ingredients clinging to sides, corners & bottom of pan. Bake 40-45 minutes until pick inserted near center comes out clean. Cool in pan on rack. Just before serving dust with confectioners' sugar.