Preheat oven to 350°F. Butter bottom and sides of an 8 x 12 inch baking dish with 1 tablespoon butter or spray with cooking spray. Set aside.
In a large pot, cover cubed potatoes with cold water. Season water with 1 teaspoon salt. Bring to a boil cooking over medium-high until fork-tender, about 12-15 minutes. Drain well.
Return potatoes to pot. Using an electric mixer whip in 4 tablespoon butter, half & half, 1 teaspoon salt, garlic powder, onion powder, pepper and nutmeg. Whip for 2 minutes or until creamy and combined. Add additional half & half as needed while whipping. Taste and adjust salt to your taste.
By hand, stir in 1½ cups shredded cheese, garlic-herb cheese spread, and chives. Stir until fully combined.
Spread potatoes into dish. Sprinkle the top with remaining shredded cheese. May bake immediately or, cover with plastic wrap and refrigerate for several hours or overnight.
If chilled, remove from refrigerator at least 30 minutes before baking. Dot the top with the remaining 1 tablespoon of butter, then place into the preheated oven.
Bake for 40-45 minutes or until the top is golden and potatoes are heated through. Let stand 5 minutes, then serve.