Step 1

Preheat the oven to 425 degrees F.

Step 2

Grease a 3-quart casserole dish with butter.

Step 3

Poke each potato with a fork all over, about 3-4 times.

Step 4

Place the poked potatoes on a sheet tray.

Step 5

Roast until the potatoes are tender when pressed with tongs, about 55 minutes to 1 hour and 10 minutes.

Step 6

Transfer the roasted potatoes from the oven and lower the oven temperature to 375 degrees.

Step 7

While the potatoes are roasting, in a large skillet over medium heat, work in two batches to cook the bacon until golden and crispy, about 6-8 minutes per batch.

Step 8

Let the cooked bacon drain on a paper-towel-lined plate.

Step 9

Once the bacon is cool, crumble or chop into small pieces.

Step 10

In a large bowl, place the melted butter, the cream cheese, the warm milk, the sour cream, the salt, and the pepper.

Step 11

Once the potatoes are cool enough to handle, cut them in half lengthwise.

Step 12

Scrape the flesh out of the skins from the potatoes and scoop them into the milk mixture bowl.

Step 13

Mash the potatoes and the milk mixture together with a potato masher. Be careful not to over-mash or it will ruin their texture.

Step 14

Fold in 1/2 of the bacon, 1/2 of the cheddar cheese, the parmesan, and 1/2 of the chives.

Step 15

Transfer the potato mixture into the prepared baking dish.

Step 16

Bake, covered with foil, until the edges are bubbly, about 35 minutes.

Step 17

Top the potato mixture with the remaining bacon and the remaining cheddar cheese.

Step 18

Bake, uncovered, until warmed through and lightly golden, about 15-20 minutes.

Step 19

Let the casserole rest for 10 minutes, then top with the remaining chives.

Step 20

Serve.