Preheat your oven to 400°F (200°C). Scrub the russet potatoes thoroughly and pierce them with a fork several times. Bake the potatoes directly on the oven rack for about 45-60 minutes, or until they are tender when pierced with a fork.

In a large skillet over medium heat, add the ground beef or lamb. Cook until browned, breaking it apart with a spatula, about 5-7 minutes. Drain excess fat if needed.

Add the diced onion and minced garlic to the skillet. Sauté for 2-3 minutes until the onion is translucent. Mix in the mixed vegetables, beef broth, tomato paste, Worcestershire sauce, thyme, salt, and pepper. Let it simmer for about 10 minutes until the mixture is slightly thickened.

Once the baked potatoes are done, remove them from the oven and let them cool slightly. Cut them in half lengthwise and scoop out some of the insides into a mixing bowl. Add butter and milk to the potatoes and mash until creamy. Season with salt and pepper.

Preheat your oven to 375°F (190°C). In a baking dish, place the meat and vegetable mixture as the bottom layer. Spoon the mashed potatoes over the meat, spreading evenly. Sprinkle the shredded cheddar cheese on top.

Bake in the oven for 20-25 minutes, or until the cheese is melted and bubbly and the edges are golden brown.

Allow the dish to cool for a few minutes before serving. Garnish with fresh herbs if desired.