Brown the beef. In a large pot over medium-high heat, cook the ground beef until fully browned. Drain excess grease.
Cook vegetables. Add the celery, carrots, and onion to the pot. Stir and cook for about 5 minutes, until slightly softened.
Add potatoes. Stir in the chopped potatoes until evenly combined.
Season and thicken. Sprinkle the flour, salt, garlic powder, Italian seasoning, and black pepper over the mixture. Stir well to coat everything evenly.
Add tomato paste. Stir in the tomato paste until fully incorporated.
Simmer soup. Pour in the beef broth and stir until smooth. Bring to a boil, then reduce heat to medium-low and simmer for about 20 minutes, or until the potatoes and vegetables are fork-tender.
Notes
Tomato base. Tomato paste can be replaced with 1 to 2 cups of leftover spaghetti sauce.
Vegetable swaps. Mushrooms should be added with the onions. Softer vegetables like zucchini can be added with the potatoes.
Potato timing. Russet potatoes cook faster than yellow or red potatoes. Smaller chunks cook more quickly, so begin checking for doneness after 10 minutes.
Storage. Store leftovers in an airtight container in the refrigerator for up to 5 days.