1Heat oven to 350°F. In 13x9-inch pan, melt butter in oven. Pour walnuts with syrup over butter, spreading evenly to cover bottom of pan.
2In medium bowl, toss pears with cinnamon-sugar until evenly coated. In large bowl, beat cake mix, oil, eggs and pear nectar with electric mixer on low speed 30 seconds. Beat on medium speed 2 minutes, scraping bowl occasionally. Fold in pears. Pour batter over nuts in pan.
3Bake 45 to 50 minutes or until toothpick inserted in center comes out clean. Immediately run knife around sides of pan to loosen cake. Place heatproof serving plate upside down on pan; turn plate and pan over. Let stand 5 minutes; remove pan. Cool 30 minutes. Serve warm or cool. Store covered in refrigerator.