In medium sauce pot, melt butter over medium high heat. Add onions and cook, stirring often, until caramelized and lightly browned, about 20 minutes. If you'd like, stir in dried basil and cook a minute or two more.
In 2 cup measuring cup, add 1 cup cold water and packet of gravy mix. Stir vigorously with a fork until well combined and smooth. Pour into pot along with remaining 2 cups of water. Bring to a boil while stirring often.
Once boiling, reduce heat and simmer about five minutes. Serve immediately or follow instructions below if you'd like to serve it restaurant style.
Optional Restaurant style instructions:
Divide soup among four oven safe bowls, top each with a piece of toasted bread and a nice sprinkling of mozzarella. Place on baking sheet and put in oven under a low broiler just until lightly browned on top (3-4 minutes). Serve immediately.