This is a new one for me, I never heard of it, but seems to be a popular ingredient in many recipes. Here is a shortcut, you know what goes in it exactly. This makes basically 1 can of Condensed Cream of Onion Soup.
Most recipes will just call for a can of condensed soup, some recipes (or if you just want to make the soup by itself) call for plus 1 can of water. One can equals 1ΒΌ cups of water. But as a healthier alternative to using water, try using whey if you recently made cottage cheese, or water used to boil potatoes. Milk can also be used in place of water to make a creamier soup.