Preheat your oven to 350°F and grease a 9x13-inch baking dish well.
In a large bowl, combine the cake mix, coconut pecan frosting, eggs, oil, and milk. Beat with an electric mixer until smooth.
Stir in the ½ cup of chopped pecans, then pour the batter into the prepared pan. Bake for 30 to 40 minutes, until a toothpick inserted in the center comes out clean or with just a few moist crumbs.
While the cake is still warm, use the handle end of a wooden spoon to poke holes all over the top, going about halfway down rather than all the way through.
Melt the butter in a saucepan over medium heat, then add the sweetened condensed milk and stir well. Bring to a gentle simmer, then stir in the remaining ½ cup of chopped pecans. Remove from heat.
Slowly pour the warm sauce over the warm cake, letting it seep into the holes and run down the sides.
Refrigerate the cake for at least an hour before slicing.