Bring the soup to a boil over high heat. Reduce the heat to low and simmer, covered, for 10 minutes.
Taste the soup and adjust the seasonings if needed, then serve.
Video
Notes
You can omit the sausage and add small meatballs instead. If using cooked meatballs, add them to the hot soup after it has finished cooking. If they're raw, add them to the soup right before you boil it, and check to ensure they are cooked through before serving.
Seasonings, especially salt, are just guidelines and should be adjusted to taste. I prefer salted broth, as I find low-sodium broth lacking in flavor. But you can use it if you'd like. Then, taste the soup and decide if it needs more salt.
The leftovers keep well for 3-4 days in the fridge in an airtight container. I gently reheat bowls or mugs of them, covered, in the microwave at 50% power. If reheating on the stovetop, add 1-2 tablespoons of water. You can also freeze individual servings in freezer-safe mason jars. To reheat, remove the metal lid, cover with a microwave-safe plate, and quickly reheat in the microwave.