Ingredient:

• 3 pounds Yukon Gold potatoes
• 1 tablespoon kosher salt
• ¼ cup milk
• 3 tablespoons salted butter, divided
• 1 cup shredded white Cheddar cheese
• ¼ cup sour cream
• 1 large egg yolk
• 2 teaspoons kosher salt, divided
• 1 teaspoon ground black pepper, divided
• 1 tablespoon olive oil
• 1 cup diced onion
• 1 cup diced carrot
• 1 pound ground lamb
• 1 pound ground beef sirloin
• 3 tablespoons all-purpose flour
• 1 teaspoon finely chopped fresh rosemary
• 1 teaspoon finely chopped fresh thyme
• 1 cup beef stock
• 1 tablespoon tomato paste
• 1 tablespoon Worcestershire sauce
• 1 cup frozen green peas
• 1 tablespoon chopped fresh parsley, or to taste