Preheat oven to 350°F. Lightly grease or butter a 9”x 13” baking dish; set aside.
In a medium mixing bowl, scoop out 4 potatoes and mash lightly until a consistent size. In a separate medium mixing bowl, repeat with remaining 6 potatoes.
Combine salt, garlic powder, and black pepper in a small bowl. Sprinkle1 1/4 teaspoons of the seasoning over the potatoes in the medium bowl; toss to combine. Repeat with the remaining seasoning and the potatoes in the large bowl.
In a medium bowl, stir together sour cream and softened cream cheese.
Measure out and reserve 3 tablespoons chopped bacon and 1/2 cup cheddar cheese.
Using the seasoned potatoes from the larger bowl, layer one-half of the potatoes in the bottom of baking dish, followed by 1 cup sour cream mixture, half of the bacon and half of the cheese. Repeat layer once more.
To the remaining seasoned potatoes, add the remaining sour cream mixture, 1/2 cup milk, and reserved 1/2 cup of cheddar cheese. Use a hand mixer and beat until fairly smooth, adding more milk if necessary. Scoop potato mixture into a pastry bag fitted with a large star tip. Pipe swirls over the top of the casserole.
Bake uncovered in preheated oven for 35 -45 minutes, or until golden brown and hot in the center. Remove from oven and garnish with reserved 3 tablespoons of bacon and chopped chives. Serve immediately.