Preheat oven to 350 degrees. Peel potatoes, and cut into 1-inch chunks. Place in a large saucepan, and add enough cold water to cover by about 2 inches. Bring to a boil over medium-high heat, and reduce to a simmer. Cook until tender, about 20 minutes. Drain; return to pan, cover, and set aside.
Meanwhile, heat a large skillet over medium heat. Add bacon, and cook until crisp. Transfer to paper towels to drain; let cool, and crumble into pieces.
Using a fork, mash the potatoes in pan until light and fluffy. Add the cream cheese, butter, and sour cream, and stir until combined and smooth. Add the chives, 2 cups cheddar cheese, half the bacon, salt, and pepper. Stir until well combined.
Scoop into a 9x13" baking dishe. Top with remaining 1/2 cup cheddar cheese. Bake until top is slightly golden and potatoes are heated through, about 30 minutes. Remove from oven; garnish with remaining bacon and more green onions. Serve immediately.
To make the day before, simply do steps 1-3 and then place in a baking pan and cover. Keep refrigerated. When you're ready to serve it, simply uncover and follow step 4!
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