Preheat oven to 325 degrees F. Place the cake mix, butter and 1 egg in lg. mixing bowl. Blend with electric mix on low speed for 1 minute or until well combined and thick.
Measure out 2/3 of the batter and reserve. Put remaining batter into bottom of ungreased 13 x 9 inch baking pan and place in oven. Bake until crust is light brown and puffs up (around 15 minutes) Remove pan from oven (leave oven on) and let cool for about 10 minutes.
Place reserved crust mixture, corn syrup, remaining 3 eggs and vanilla in same mixing bowl. Blend for 1 minute on low. Scrape down bowl. Increase speed to medium until well combined. Fold in the pecans until they are well distributed.
Pour mixture on top of cooled crust, smoothing out with rubber spatula. Bake until edges are browned but center is still a little soft (40 to 45 minutes). Let cool for 30 minutes. Serve with ice cream or whipped cream