Instructions

For potatoes:

1. Place diced potatoes in large pot and cover with cold water. Set pan over high heat, cover and bring to boil. 
2. Once water is boiling, uncover pot, and decrease heat to maintain simmer. Cook potatoes for 10 to 15 minutes or until tender and easily crushed with fork. (While potatoes are cooking, prepare meat filling, below.)
3. Place half-and-half and butter in small saucepan over low heat. Warm, stirring occasionally, until butter is melted.
4. Drain potatoes in colander, then return to hot pot. Using potato masher, coarsely mash potatoes.
5. Add half-and-half, butter, salt and pepper; continue to mash until smooth.
6. Stir in cheese and egg yolk until well-combined.

For filling:

1. Preheat oven to 400F and spray 10-by-8-inch baking dish with cooking spray.
2. Heat oil in 12-inch sauté pan set over medium-high heat.
3. When oil shimmers, add onion and carrots; sauté for 3 to 4 minutes or just until lightly brown. Add garlic and stir to combine.
4. Add lamb, salt and pepper to onion mixture. Cook, stirring occasionally, for about 3 minutes or until lamb is browned and cooked through. Drain off some fat.
5. Sprinkle lamb mixture with flour and toss to coat, continuing to cook for another minute.
6. Add tomato paste, chicken broth, Worcestershire, rosemary and thyme, stirring to combine. Bring to boil.
7. Reduce heat to low, cover and simmer slowly for 10 to 12 minutes or until sauce is thickened slightly.
8. Add corn and peas to lamb mixture and spread evenly into prepared baking dish.
9. Top lamb mixture with mashed potatoes, starting around inside edges of dish, then covering lamb mixture in center. This creates seal to prevent mixture from bubbling up over potatoes when cooking.
10. Smooth potatoes with rubber spatula.
11. Place baking dish on parchment-lined sheet pan on middle rack of oven. Bake for 25 minutes or until potatoes begin to brown.
12. Transfer baking dish to wire rack and cool for at least 15 minutes before serving.