Preheat oven to 350°. Grease a 15x10x1-in. baking pan. In a large bowl, beat the first 6 ingredients until well blended. In another bowl, whisk flour, baking powder, pie spice, baking soda and salt; gradually beat into pumpkin mixture., Transfer to prepared pan. Bake 18-22 minutes or until a toothpick inserted in center comes out clean. Cool completely in pan on a wire rack., In a small heavy saucepan, melt butter over medium heat. Heat 5-7 minutes or until golden brown, stirring constantly. Transfer to a large bowl. Gradually beat in confectioners’ sugar, vanilla and enough milk to reach desired consistency. Spread over bars; let stand until set.