Boil 2 tbs russet potatoes in salted water until tender, about 15–20 minutes. Drain and mash with ¼ cup butter and ½ cup whole milk until smooth. Season with Salt and pepper. Set aside.
2 tbs russet potatoes, ¼ cup butter, ½ cup whole milk, Salt and pepper
Heat 2 tbsp olive oil in a large skillet over medium heat. Add 1 medium onion, 2 medium carrots, and 2 cloves garlic; sauté until softened, about 5 minutes.
1 medium onion, 2 cloves garlic, 2 medium carrots, 2 tbsp olive oil
Add ground ½ lb ground lamb and ½ lb ground beef. Cook, breaking up the meat, until browned and cooked through. Drain excess fat if necessary. Stir in 2 tbsp tomato paste, 1 tbsp Worcestershire sauce, 1 tsp fresh thyme leaves, 1 tsp fresh rosemary, and season with Salt and pepper.
½ lb ground lamb, ½ lb ground beef, 2 tbsp tomato paste, 1 tbsp Worcestershire sauce, 1 tsp fresh thyme leaves, 1 tsp fresh rosemary, Salt and pepper
Pour in 1 cup beef broth and let simmer until slightly thickened, about 5–7 minutes. Stir in 1 cup frozen peas and remove from heat.
1 cup beef broth, 1 cup frozen peas
Preheat oven to 400°F (200°C). Spread the meat filling evenly in a 9x9-inch (or similar) baking dish. Spoon mashed potatoes on top, spreading to cover the filling completely. Sprinkle grated 1/2 cup manchego cheese in an even layer.
1/2 cup manchego cheese
Bake for 20–25 minutes, until the mashed potatoes are slightly golden on top and the filling is bubbling. Let rest 5 minutes before serving.