Preheat your oven to 350°F. Lightly spray a 9x13-inch baking dish with nonstick cooking spray.
In a medium bowl, mash 4 ripe bananas until mostly smooth. You want a few little lumps for texture. Stir in (1) 14-ounce can of sweetened condensed milk and 1 teaspoon pure vanilla extract until fully combined.
Then spread the mixture evenly into the bottom of your prepared baking dish. If you're using pecans, sprinkle ¼ cup over the top of the banana layer.
Sprinkle the contents of the cake mix packet evenly over the banana base. Do not stir.
Drizzle ¾ cup of melted salted butter over the cake mix layer, doing your best to moisten the surface evenly.
Sprinkle half of the included cinnamon swirl packet over the top of the melted butter.
Place in your preheated oven and bake for 45–50 minutes, or until the top is golden and bubbling and a cake tester or toothpick comes out mostly clean.
While the cake is baking, make the caramel sauce. Combine ½ cup brown sugar and 3 tablespoons salted butter in a small saucepan over medium heat. Stir until melted and bubbling, about 2–3 minutes.Remove from heat and stir in 2 tablespoons heavy cream and ¼ teaspoon pure vanilla extract. Whisk until the sauce is smooth. Let it cool slightly—it thickens as it sits.
Once the cake has cooled for 10–15 minutes, slice and serve warm. Drizzle with the caramel sauce and a handful of extra chopped pecans just before serving. ENJOY!