Preheat oven to 425°F. Place potatoes on a baking sheet.
Brush each with olive oil, sprinkle with salt, and prick with the tines of a fork.
Bake for 45-60 minutes or until fork-tender. Lower oven temperature to 350°F.
Meanwhile in a large hot skillet, add the beef, onion, and salt and cook until the beef is browned, breaking it into pieces with a spatula as it cooks. Drain off any excess grease.
Add the garlic and cook 30 seconds.
Add the tomato sauce and vegetables. Cook for 4-5 minutes, stirring often.
Add the broth and Worcestershire sauce and bring to a boil. Turn down the heat and simmer for 15-20 minutes or until the mixture is thick and glossy, stirring often. Add the rosemary.
Once the potatoes are done cooking, cut in half lengthwise. Scoop out the insides into a large mixing bowl, being careful not to tear the shell. Place the hollowed potato shells back onto the baking sheet.
With an electric mixer or by hand with a potato masher, beat the cooked potato insides until mashed and smooth (do not overbeat). Beat in the butter and salt until completely incorporated then slowly beat in the milk. Stir ½ cup cheese.
Divide the meat mixture among the potato shells. Top with mashed potatoes then sprinkle with the remaining ¼ cup cheese.
Bake at 350°F for 18-20 minutes or until golden brown and cheese has melted.