1. Start by placing the diced potatoes in a large pot, covering them with water, and adding 3/4 teaspoon of salt. Bring the water to a boil and cook the potatoes until tender, about 15 minutes. Drain the potatoes, then mash them with the sour cream and 1 tablespoon of butter. Set the mashed potatoes aside.

2. In a large soup pot, cook the ground beef over medium heat until browned. Drain any excess grease, then remove the beef from the pot and set it aside.

3. Melt the remaining 2 tablespoon of butter in the same pot. Add the diced onion and sauté until softened, about 5 minutes. Stir in the minced garlic and cook for an additional minute.

4. Sprinkle the flour over the onion mixture and stir for 1-2 minutes. Slowly whisk in the chicken broth until the mixture is smooth and free of any lumps.

5. Stir in the half and half, Worcestershire sauce, Italian seasoning, mustard powder, and ground sage. Bring the soup to a simmer.

6. Return the cooked ground beef to the pot, then stir in the mixed frozen vegetables and shredded cheddar cheese. Simmer the soup for 10 minutes, allowing the flavors to meld.

7. Finally, stir the mashed potatoes into the soup until fully combined and creamy.

8. Adjust the seasoning with salt and pepper to taste. Ladle the Shepherd’s Pie Soup into bowls and serve hot, with crusty bread on the side for dipping.