I love a simple recipe that has delicious results. These are a sweet chewy caramely surprise!
1 box yellow cake mix
4 Tbl butter softened
2 eggs, divided
1 (14 oz) can sweetened condensed milk
1 tsp vanilla
1/2 cup finely chopped walnuts
1/2 cup toffee bits
Preheat oven to 350°. Spray 9×13 pan. Combine cake mix, butter and one egg, mix until crumbly. Press mixture into bottom of pan, set aside. Combine milk, remaining egg, vanilla, walnuts, and toffee bits. Pour and gently spread over cake mix in pan. Bake for 35 minutes, cover with foil during baking to prevent getting too brown. Cool completely and cut into bars.
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Cookies Cakes Pies Oh My 
I have a similar recipe and it is so good. Try using butter pecan cake mix and you will love it!
Great idea, thanks!