Here is a great mashed potato recipe from foodnetwork. If needed, you can thin the end product with cream, as needed.

1/2 cup butter (8 tablespoons or 1 (4-ounce) stick
6 scallions, white parts only (use tender green parts for garnish below), finely sliced
6 large potatoes, peeled and cut into chunks
Salt
White pepper
2 cups sharp shredded Cheddar
Tender green parts from scallions above, finely chopped or 1/4 cup chopped fresh chives

Take 1 tablespoon of the butter and add to a small fry pan, then saute the white parts of the scallions until soft. In a large sauce pot, boil the potatoes until they are tender. Drain the potatoes well, add the sauteed scallions, then mash and whip in butter, salt and white pepper, to taste, with a beater. Fold the cheese into the potatoes and allow it to melt. Stir to evenly distribute cheese, transfer to a serving dish and garnish with finely chopped tender green parts of scallions or fresh chives.