2 lbs. sweet potatoes or yams 2 lbs. Russet potatoes 8 oz. cream cheese, divided into 2 oz. pieces at room temperature 4 oz. unsalted butter, divided use freshly ground black pepper
Cut potatoes into cubes and boil in separate pots. When potatoes are fork tender, drain, except for about a 1/3 cup of the water from each to use in case you need extra moisture.
Mash each batch of potatoes separately with 2 oz. of butter and 4 oz. of cream cheese. Add some of the cooking water if necessary. Mash until creamy and smooth (I use a hand mixer).
Using a large spoon or an ice cream scoop, layer alternating dollops of each type of mashed potato in a glass baking dish. When you’ve filled the dish, take a sharp knife and “marble” the potatoes. Bake in a 350 oven for about 40 minutes until hot throughout. If you like, you can top the mixture with your favorite grated cheese, melting it during the last 5 minutes of baking.