• Peel and cube Yukon gold potatoes and add to a pot of water. Add 1 tsp salt and simmer until fork tender. Drain.
• In a large bowl add sour cream, egg yolk and half and half. Whisk. Add the potatoes and hand mash. Do not use a mixer! Set aside.
• Put the oil in a large pan and add the ground beef and the onions. Salt and pepper. Cook the ground beef and onions until there is no pink left in the meat. Add the garlic and cook for 2 minutes. Drain off the excess fat. Set aside.
• In a small saucepan, melt 2 TBS butter over medium heat. When the butter is melted add the flour and whisk. Cook for a couple minutes so the flour looses it's raw taste. Add the beef stock and whisk until thickened. Add in the Worcestershire sauce and kitchen bouquet. Whisk to incorporate.
• Remove the gravy from the heat set aside.

To assemble

• Put the ground beef mixture in the bottom of a casserole dish. Add the gravy. Top with the peas and then the potatoes.
• Bake at 350 ° until bubbly and hot, about 30-40 minutes. If the mashed potatoes are not browned broil them for a couple minutes.