Spray a 9x13-inch casserole dish with nonstick spray. Set aside.
Peel the potatoes and cut them into 1-inch cubes. Place the potatoes in a large Dutch oven and cover with 1-inch water. Add 2 teaspoons kosher salt, 1 teaspoon ground black pepper, 1 teaspoon granulated onion, and ½ teaspoon garlic powder; stir well. Set over high heat and bring to a boil, then reduce heat to low and simmer until potatoes are fork tender, about 15 minutes.
5 pounds Yukon Gold potatoes, 1 tablespoon kosher salt, 1½ teaspoons ground black pepper, 1 teaspoon granulated onion, ½ teaspoon garlic powder
Drain the potatoes and return to the empty, still hot pot. Set the pot over low heat to boil off excess moisture from the potatoes – this should take just about 1 minute.
Mash the potatoes, then and add the butter, cream cheese, sour cream, half-and-half, and 1 cup cheese. Stir well. Add half of the bacon and 1 tablespoon chopped chives. Stir well. Taste and, if needed, season with additional kosher salt and black pepper.
½ cup unsalted butter, 4 ounces cream cheese, 1½ cups half-and-half or heavy cream, 2 cups shredded Cheddar cheese, 1 pound bacon, 2 tablespoons chopped fresh chives, 1 cup sour cream
Spread the mashed potatoes into the prepared baking dish.
At this point, the potatoes can be cooked immediately or refrigerated up to 2 days.