Hydrate onion by placing it in a small heatproof cup, barely covering with water, and heating very briefly in the microwave. It will bubble up suddenly, after just a few seconds, so be ready to shut it off. Give it a few minutes to absorb the water, while you gather the rest of your ingredients.
Add the onion to a soup pot with the butter. Heat gently on low, while you open cans. Do not cook it beyond a golden color.
Stir in the rest of the ingredients, EXCEPT for the dried potato flakes.
Bring to a boil, and turn to low. At this point, you can either move on to the next step, or let it simmer on very low for up to 30 minutes. Any longer than that, and the vegetables get too mushy.
Bring soup to a boil again, and stir in the dried potato flakes. Cook 5 more minutes, or until the soup thickens.