Preheat the oven to 325°F (160°C). Grease a 9x13-inch baking dish with butter or non-stick spray.

Spread 2 cups of chopped pecans on a baking sheet and toast in the preheated oven for 5–7 minutes until fragrant, watching closely so they do not burn. Remove and set aside.

In a medium saucepan over medium heat, combine the corn syrup, dark brown sugar and 1/3 cup butter. Stir constantly until the butter has melted and the sugar has completely dissolved, about 3–4 minutes.

Remove the saucepan from the heat and let the mixture cool for 3 minutes. Whisk in the beaten eggs, vanilla extract and salt until the filling is glossy and smooth.

Scatter the toasted pecans evenly over the bottom of the prepared baking dish. Pour the warm filling mixture over the nuts, spreading it into an even layer.

Sprinkle the dry yellow cake mix evenly over the surface of the filling; do not stir.

Drizzle the melted 1/2 cup butter evenly over the cake mix, then sprinkle the remaining 1/2 cup pecan halves across the top.

Bake for 40–45 minutes, or until the top is deep golden brown and the edges are bubbling. Remove from the oven and allow the cake to cool for at least 15 minutes so the filling can set before serving.