Boil potatoes in salted water until tender, about 12 minutes. Drain potatoes and pour them into a bowl. Combine sour cream, egg yolk and cream. Add the cream mixture into potatoes and mash until potatoes are almost smooth.
While potatoes boil, preheat a large skillet over medium high heat. Add oil to hot pan with beef or lamb. Season meat with salt and pepper. Brown and crumble meat for 3 or 4 minutes. If you are using lamb and the pan is fatty, spoon away some of the drippings. Add chopped carrot and onion to the meat. Cook veggies with meat 5 minutes, stirring frequently. In a second small skillet over medium heat cook butter and flour together 2 minutes. Whisk in broth and Worcestershire sauce. Thicken gravy 1 minute. Add gravy to meat and vegetables. Stir in peas.
Preheat broiler to high. Fill a small flameproof rectangular casserole with meat and vegetable mixture. Spoon potatoes over meat evenly. Top potatoes with paprika and broil 6 to 8 inches from the heat until potatoes are evenly browned. Top casserole dish with chopped parsley and serve.