In a large skillet, cook the chopped onions over medium heat until softened. Add the ground beef and ground lamb, cooking until browned. Drain excess fat.

Add Vegetables and Seasoning

Stir in the peas, carrots, garlic, beef broth, Worcestershire sauce, salt, and black pepper. Simmer for about 10 minutes until the vegetables are tender and the mixture has thickened.

Make the Mashed Potatoes

In a large pot, boil the cubed potatoes until tender, about 15 minutes. Drain and return to the pot. Add butter, milk, and salt, then mash until smooth and creamy.

Assemble the Pie

Preheat the oven to 400°F (200°C). Spread the meat filling in an even layer in a baking dish. Top with the garlic mashed potatoes, smoothing them out with a spatula. Sprinkle the shredded cheddar cheese on top.

Bake

Bake in the preheated oven for 20-25 minutes, or until the cheese is bubbly and golden brown. Let it cool slightly before serving.