Preheat your oven to 350 °F (about 175 °C). Spray a 9 × 13 inch baking pan with non stick spray and set it aside.

In a medium bowl, combine 1 cup brown sugar, the corn syrup, ½ cup of the melted butter, the eggs, and vanilla. Whisk until well blended.

Stir in 3 cups of pecan halves. Spread this pecan sugar mixture evenly into the prepared baking pan.

Sprinkle the dry yellow cake mix evenly over the pecan filling. Do not stir it in.

Drizzle the remaining ¾ cup of melted butter over the dry cake mix layer.

Sprinkle the remaining ½ cup brown sugar over the butter layer.

Pour the hot water evenly over the top of the cake mix and butter. You can tilt the pan gently to help distribute the water but don’t stir.

Sprinkle the remaining 1 cup pecan halves on top of the water layer.

Bake in the preheated oven for about 30–35 minutes, or until the top is golden brown and the center is just slightly jiggly—it will firm up as it cools.

Allow the cake to cool completely before serving.

Optional: Serve with ice cream or whipped cream, and drizzle with caramel topping for extra indulgence.