Start by preheating your oven to a cozy 350°F (175°C). Meanwhile, liberally grease a 9x13-inch baking dish, setting the stage for your delectable masterpiece.

In a voluminous mixing bowl, amalgamate the butter pecan cake mix, coconut pecan frosting, eggs, oil, and milk. Utilize an electric mixer to beat this motley collection into a uniform batter. This is where art meets science.

Gently fold in the chopped pecans, ensuring they're evenly distributed throughout the batter. This adds a layer of crunch that contrasts beautifully with the cake's innate fluffiness.

Effortlessly pour your now-pecan-infused batter into your pre-prepared baking dish. Slide it into the oven and bake until a toothpick, when inserted into the cake's center, emerges free of wet batter—roughly between 30 and 40 minutes.

Once baked, remove your culinary creation from the oven. Take the rounded end of a wooden spoon and pierce holes throughout the cake's surface. It may seem counterintuitive, but this will allow the sauce to permeate more effectively.

Now, turn your attention to the sauce. In a medium saucepan over medium heat, melt the butter like a culinary alchemist. Incorporate the sweetened condensed milk and stir. Achieve a gentle simmer and introduce the chopped pecans to the mix.

With your sauce now teeming with flavor, remove it from the heat. Drizzle it delicately over your poked cake, ensuring it infiltrates the holes and drizzles down the sides. The synergy of flavors and textures at this stage is truly transformative.

Exercise patience as the cake cools, allowing the sauce to settle in. Once cooled, slice it into generous portions and prepare for a gastronomic adventure.