Preheat oven to 325° and liberally grease a 10" bundt pan with butter or non-stick spray. Set aside.
To a large mixing bowl, add the cake mix, eggs, sour cream, oil, sugar, milk, and vanilla. Use a hand mixer to beat at medium speed for 2 minutes. Stir in 1 cup chopped pecans until evenly distributed.
Pour the cake batter into the prepared pan and bake for 50-60 minutes or until a toothpick inserted into the center comes out clean. Remove from oven and let cool for at least 10 minutes before flipping.
To Make the Glaze
Heat a medium skillet over medium heat and add ¼ cup butter and chopped pecans. Cook until the pecans are toasted, stirring often.
In a medium bowl, add the powdered sugar, vanilla, melted butter, and water. Whisk together until smooth. Pour in the toasted pecans and stir to distribute. If too thick, thin with water, 1 Tablespoon at a time, until it reaches your desired consistency.
Once cake is cooled, flip it over to a cake plate or stand and pour the glaze evenly over the top.
Slice & serve!
Cake will serve 12-16 depending on how generously slices are cut.Store the cake at room temperature, covered, for up to 4 days.Cake can be frozen when wrapped tightly in plastic wrap, placed in a freezer bag, and stored in the freezer for up to 3 months.