In a large pot add the potatoes. Cover with room temperature water so the water covers the potatoes by an inch or 2. Add 2 tablespoons of salt and stir together.
Set the pot on the stove over medium-high heat until the water reaches a boil. Reduce the temperature to keep a steady boil that doesn’t overflow.
Boil until the potatoes are fork tender. The amount of time it will take to cook the potatoes will depend on how large your pieces are, about 15 minutes.
Remove from the heat and drain in a large colander and preheat the oven to 350 degrees F and spray a 3-4-quart casserole dish lightly with cooking spray.
While the potatoes cook, in a microwave safe bowl or liquid measuring cup, microwave the butter and cream together until warm and melted together.
Once the potatoes are draining, pour this liquid into the now empty pot where the potatoes were cooked.
Use a potato ricer to rice the potatoes back into the pot. Alternatively, you can add all the cooked potatoes back to the pot and use a potato masher, or hand mixer to mix until smooth.
Add the shredded cheeses, sour cream, parsley, salt, garlic powder, and pepper. Stir to combine. Put a lid over the pot for a few minutes to let the cheeses melt a little bit.
Add the sour cream and cheese and give it one more quick stir.
Dollop into the casserole dish and spread so it’s even on top. Top with the remaining cheese and bake for about 10-15 minutes or until the cheese is melted.
Remove from the oven, garnish with parsley, and serve hot.