Spread the potatoes in a large (about 9 x 13 inches) casserole, sprinkle this first layer abundantly with salt and pepper.
Add chicken on top of the potatoes, also in one single layer. Salt and pepper the chicken layer as well.
Now evenly spread butter pieces, ham and cheese across the entire surface. Sprinkle with scallions.
Pour the heavy cream over top of casserole. Salt and pepper this layer.
Cover the casserole with aluminum foil, place it in the oven (on the second shelf from the bottom) and bake for 30 minutes. Uncover the pan and bake for another 30 minutes. Remove from the oven and serve immediately.