Preheat oven to 350 degrees F. Line a 13x9x2-inch baking pan with foil, extending foil over the pan edges. Coat foil with nonstick cooking spray; set aside. In a large bowl, use a pastry blender to cut 1/2 cup butter into cake mix until mixture resembles coarse crumbs. Press mixture evenly onto the bottom of the prepared pan. Bake in the preheated oven for 15 to 20 minutes or until lightly browned and set.

Meanwhile, in a large bowl, combine eggs, brown sugar, corn syrup, the 1/3 cup melted butter, vanilla, and cinnamon; whisk to combine. Stir in mixed nuts. Pour nut mixture over warm crust. Bake about 30 minutes more or until bubbly around the edges and golden brown. Cool in pan on a wire rack. Using the edges of the foil, lift the uncut bars out of the pan. Cut into bars. Makes 32 bars.

Layer bars between sheets of waxed paper in an airtight container; cover. Store in the refrigerator for up to 1 week or freeze for up to 3 months.