1.Place potatoes in a medium pot cover with water by 1-inch and season water with 1 tablespoon salt. Bring to a boil over medium-high heat. Let gently boil until potatoes are fully tender when pierced with a fork, about 10 - 15 minutes. Drain in a colander and rinse under hot water for about 5 seconds to remove excess starches. Put potatoes back into the same pot.
2.Melt 5 tablespoons butter in the microwave and add to potatoes along with cream and sour cream. Mash potatoes with a masher while seasoning with 2 teaspoons salt and dash ground black pepper. Cover and set aside.
3.Melt 1 tablespoon butter in a 12-inch cast iron skillet. Add onion, carrots, celery and saute for about 6 minutes. Add garlic and saute 1 minute longer. Add ground beef and break until no longer pink, about 6 minutes.
4.Add flour and tomato paste and saute 1 minute. Pour in red wine, beef broth, Worcestershire, thyme and rosemary. Bring to a simmer stirring frequently. Reduce heat to low and let simmer until reduced by about 2/3, about 8 - 10 minutes.
5.Stir in peas and parsley and heat through, about 1 minute. Season filling with salt and pepper to taste. Spread beef filling into an even layer. Dollop spoonfuls of mashed potatoes evenly over top then spread into an even layer. Run a fork along top to create a pattern of wavy rows.
6.Move oven rack about 5-inches below broiler and preheat broiler to high. Transfer to oven and let broil until golden brown on top about 4 - 6 minutes (keep a close on it as every oven varies). Let rest a few minutes before serving. Garnish with parsley if desired.