Add the ground beef to a Dutch oven or soup pot over medium-high heat. Cook until browned, breaking the meat up as you go along (about 8-10 minutes).
Once the beef has browned, take it out of the pot and transfer it to a paper towel lined plate. Discard most of the fat from the pot.
Add the butter and onions to the pot, and sauté for 5 minutes.
Add in the garlic, Italian seasoning, and tomato paste, and cook for about a minute, stirring nearly constantly.
Add in the chicken broth, Worcestershire sauce, cream, potatoes, and cooked beef. Increase the heat to high and bring the soup to a boil. Once it's boiling, reduce the heat to a rapid simmer so it's gently boiling.
Cook, with the lid slightly open, until the potatoes are tender (about 20 minutes). Stir occasionally.
I like to take my potato masher and mash the potatoes a little bit right in the pot, but if you want to leave the potatoes as-is, that's fine too.
In a small bowl, mix the cornstarch with 1 tablespoon of cold water. Add the cornstarch slurry to the soup, along with the frozen mixed vegetables, and give it a good stir.
Increase the heat to high to get it going again, then reduce the heat and simmer for another 10-15 minutes or until the veggies are tender, the broth has thickened up a bit, and the potatoes have a fall-apart texture. Stir occasionally so nothing sticks to the bottom of the pot.
Give the soup a taste and season with seasoning salt & pepper as needed (I am generous with both!).