HEAT oven to 350 degrees F. Spray a 13 x 9-inch baking pan with no-stick cooking spray.
COMBINE cake mix, butter and 1 egg in large bowl; beat at medium speed of electric mixer until mixture resembles coarse crumbs. Press evenly into prepared pan.
BAKE 15 minutes. Remove from oven; sprinkle with pecans and butterscotch chips.
BEAT sweetened condensed milk, remaining 2 eggs and vanilla in small bowl. Pour evenly over chips.
BAKE an additional 25 to 30 minutes or until center is set. Cool thoroughly. Cut into bars.
*To toast pecans: Place pecans in dry nonstick skillet; cook over medium heat, shaking pan until nuts are lightly brown.