Preheat the oven to 350 degrees.

Wash and cut all of the bad spots from the potatoes and cut them into quarters, place them into a stockpot, and fill with water until just covering the potatoes.

Add two tablespoons of kosher salt and set over high heat for twenty to twenty-five minutes or until the potatoes are soft and can be pierced with a fork. Drain off the water and place the potatoes into a large mixing bowl.

Peel the butternut squash and cut into one-inch cubes. Place the squash into a steamer pot with cups of water over med-high heat and steam for four to five minutes or until you can pierce the squash with the tines of a fork. Add the squash to the potatoes.

Add the cheeses, heavy whipping cream, sour cream, and melted to the potato and squash, using a wand mixer mash together until the ingredients are well-combined.

Next, add the two whole eggs and two egg whites and mix thoroughly. Add the smoked flaky sea salt and freshly cracked black peppercorns.

Spoon the mixture into the casserole dish and bake on the center rack for an hour, the top should be golden brown.

Remove from the oven and serve.