1Heat oven to 350°F. Spray bottom only of 13x9-inch pan with cooking spray.
2In large bowl, beat cake mix, 3/4 cup milk, the oil, eggs and sweet potatoes with electric mixer on low speed 30 seconds. Beat on medium speed 2 minutes. Stir in 1 cup chopped pecans. Pour batter into pan. Bake 20 to 25 minutes or until toothpick inserted in center comes out clean. Cool completely in pan on cooling rack, about 1 hour.
3In medium bowl, beat butter with electric mixer on medium speed until creamy. Gradually add powdered sugar, beating until light and fluffy. Beat in 1 tablespoon milk and the vanilla. Frost cake. Sprinkle with praline pecans.