Traditional Shepherd's Pie

Ingredients (21)

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