1. Place the diced potatoes in a large pot, cover with water, add 3/4 teaspoon of salt, and bring to a boil. Cook until the potatoes are tender, about 15 minutes. Drain the potatoes and 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. In the same pot, melt 2 tablespoon of butter. 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 mixture to a simmer.

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

7. Gently stir the mashed potatoes into the soup until fully combined and the soup becomes creamy and smooth.

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