In a small to medium pot, melt the butter (or the oil) over medium heat. If you have no way to blend your soup once cooked, finely chop your onion and very finely mince your garlic, otherwise, just slice it to saute it quickly.
Add the tomatoes, broth, baking soda, parsley, bay leaf and salt and pepper. Bring up to a boil, then turn down to a simmer. Simmer for 10 minutes or so over medium-low heat. The baking soda will foam up and help neutralize the acids from the canned tomatoes and you won't taste it at all.