01 -
Place a rack in the center of the oven and heat to 375 degrees F. Butter a 9x13-inch baking dish.
02 -
Cook the chopped bacon in a skillet over medium heat until browned and crisp, 8-10 minutes. Transfer to paper towels and reserve 2 tablespoons of the bacon fat.
03 -
In a saucepan, combine the reserved bacon fat, heavy cream, milk, garlic, salt, pepper, and onion powder. Warm over medium heat for 3-4 minutes, stirring often, until steamy and fragrant. Do not boil.
04 -
Slice the potatoes 1/8 inch thick. Arrange half in the baking dish, sprinkle with 3/4 cup cheddar, then repeat with the remaining potatoes and another 3/4 cup cheddar. Pour the warm cream mixture evenly over the top and press the potatoes down lightly.
05 -
Cover the dish tightly with foil and bake for 60-65 minutes, until a thin knife slides through the center with little resistance.
06 -
Remove the foil, sprinkle with the remaining 1/2 cup cheddar, and bake uncovered for 15-20 minutes, until the top is melted and lightly golden.
07 -
Let the potatoes rest for 10 minutes. Top with crisp bacon, small dollops of sour cream, sliced scallions, and chives if using. Serve warm.