Step #4 In a large mixing bowl, stir this together remaining cake mix, melted butter & 1 egg until thoroughly mixed (mixture will be crumbly).
Step #5 Press into pan.
Step #6 Bake until light golden brown (15-20 mins).
Step #7 In a large mixing bowl, remaining 3 eggs, mix reserved cake mix, maple syrup, sugar & vanilla extract; beat at lowish speed of electric mixer for 3 mins.
Step #8 Pour over crust.
Step #9 Sprinkle top with walnuts.
Step #10 Bake until filling is set (30-35 mins).
Step #11 Cool completely in pan.
Step #12 Cut into bars to serve, & store any extras in refrigerator.