Boil potatoes in salted water until tender (about 15 minutes). Drain, then mash with tallow and milk. Season to taste.
Sauté onions, carrots, and garlic in Wagyu tallow until soft. Add ground meat and cook until browned. Stir in tomato paste, Worcestershire, herbs, broth, and peas. Simmer for 5 minutes.
Assemble in baking dish: meat filling on the bottom, mashed potatoes on top. Sprinkle with cheddar.
Bake at 400°F for 20-25 minutes until golden and bubbling. If desired, broil for a crisp top.
