Preheat oven to 350°F. Spray a 13x9-inch baking dish or cake pan with nonstick cooking spray or baking spray.
In a large bowl using an electric hand mixer or in the bowl of a stand mixer fitted with the paddle attachment, combine cake mix, 1/2 cup melted butter and one large egg. Beat until fully combined then scrape from the bowl and press evenly into the bottom of the prepared dish. (This cake doesn't form a batter it will be stiff.)
In the same bowl whip together the corn syrup, reserved 3 eggs, remaining 1/4 cup melted butter, granulated sugar, brown sugar, vanilla extract and salt. Beat on medium-low speed just until combined.
Fold in the pecans by hand. Pour the pecan filling evenly over the cake mix layer.
Place into the oven and bake for 40-45 minutes or until the center is set when gently shaken. Check at 30 minutes and lay a piece of foil on top if needed, to prevent over browning.
Cool pecan pie cake completely in the pan on a wire rack.
Cut into squares and serve with a dollop of whipped cream.