Step 1

Preheat the oven to 400 degrees F. Grease a 9-by-13-by-2-inch (3.75-quart) casserole dish with butter.

Step 2

Put the potatoes in the prepared casserole dish, add the half-and-half and stir to combine. Spread the potatoes in an even layer and place the block of feta in the center, on top of the potatoes. Season with 1 tablespoon salt and a few grinds of pepper and dot the butter over the potatoes. Cover the casserole with aluminum foil and bake until the half-and-half is simmering, the cheese is bubbling and the potatoes are cooked through and very tender when pierced with a small sharp knife, about 1 hour and 20 minutes.

Step 3

Remove and reserve the aluminum foil. Use a potato masher to mash the ingredients in the casserole dish until well combined, smooth and fluffy. Fold in the sour cream and season with salt and pepper. Cover the mashed potatoes with the reserved foil and return to the oven until warmed through, about 10 minutes. Top with the chopped chives and a few grinds of pepper.