1. Set oven to 350 degrees.
2. Grease a 13 x 9 baking pan.
3. Set aside 1 cup of cake mix for the filling.
4. For the crust: In a large mixing bowl, combine the remaining cake mix, butter, and slightly beaten egg.
5. Stir with a fork until crumbly.
6. Transfer into prepared pan.
7. With lightly floured hands, press lightly and evenly into bottom of pan to form a crust (don't pack crust down to hard).
8. Bake the crust for 12 minutes (don't over bake).
9. Meanwhile, for filling, in a medium bowl, combine the second mixture of eggs, brown sugar, cornsyrup and vanilla.
10. Add the reserved 1 cup of cake mixture; stir with a fork, just until blended (do not beat, some tiny clumps will remain thats okay!).
11. Spread filling evenly over baked crust; sprinkle evenly with pecans.
12. Bake 25-30 minutes, or until the filling appears set when pan is gently shaken.
13. Cool completely on wire rack.
14. Cut into bars.