Peel and dice the potatoes. Place potatoes and 1 tablespoon of sea salt in a stock pot and cover with water. Bring to a boil and cook until potatoes are cooked. Drain.
Preheat oven to 350°F.
Mash drained potatoes, ¼ cup butter, heavy cream and milk until smooth and creamy.
Meanwhile, heat 2 tablespoons of butter, onions and carrots over medium heat in a skillet.
Saute vegetables until onions are soft and translucent. Add peas and leftover pot roast to the vegetable mixture.
Spread meat/vegetable mixture into a casserole dish. Add as much gravy as you have left in the pot. (Follow packet instructions to make extra gravy if desired and stir into the meat/vegetable mixture.)
Top with the mashed potatoes.
Sprinkle paprika, salt, pepper, and fresh thyme over the top of the casserole.
Melt remaining butter and pour over the mashed potatoes.
Bake for 25-30 minutes or until the gravy is bubbling from the bottom of the dish and the potatoes are beginning to brown.