Peel, and slice potatoes. Place in large pot, cover with water, and bring to a boil over high heat. Reduce heat to medium and simmer until potatoes are tender, but not mushy. Drain well.
Preheat oven to 400 degrees F.
Combine cream cheese and sour cream into bowl and with an electric mixer, beat until smooth. Add drained potatoes, and mix until creamy, while adding spices.
Spray baking dish (approx 13”x9”) with cooking spray. Spoon mashed potatoes into baking dish. Dot with butter. Cover with foil and bake for about 15 minutes, until butter is melted and potatoes are hot all the way through.