Preheat oven to 350 degrees F (175 degrees C). Line a deep 9-inch springform pan with aluminum foil and coat generously with cooking spray.
Whisk brownie mix, oil, 2 eggs, and water together in a bowl until well combined. Spread batter into the prepared pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 30 minutes. Remove from oven and leave oven on.
Whisk brown sugar, corn syrup, 2 eggs, bourbon, vanilla extract, and salt together in a bowl. Add melted butter slowly, whisking until well combined. Add pecans and stir to coat in the filling. Pour gently over the brownie layer; spread evenly using a spatula.
Bake in the hot oven until center is set, 30 to 35 minutes. Let cool to room temperature, at least 2 hours.