Put large dutch oven over medium heat. Dice onion and put in dutch oven along with butter and pinch of salt. Sweat 4-5 minutes. Mince garlic and add to onion, cook for another minute, and remove from pot. Set aside.
In same pot, brown meat until cooked, 7-8 minutes, along with a pinch of salt and pepper. Once cooked, add in tomato paste and cook out for another minute. Add in cooked onion and garlic, mixed vegetables, Worcestershire Sauce, red wine vinegar, chopped rosemary, corn starch (combined into the stock), and stock. Bring to simmer and cook for 5 minutes.
Turn broiler on high. Mash together the sweet potato, cheese, garlic powder, and pinches of salt and pepper. Turn stew off heat and fill oven safe bowls/baking dish. Top with the mashed sweet potatoes and broil for 2-3 minutes or until slightly brown. Serve immediately. Your bowl will be hot.
* Make it lighter with riced cauliflower, more traditional with baking potatoes.