Melt the butter in a saucepan over medium heat. Add the onions just before the butter is fully melted and sautee them briefly. Turn down to medium-low heat and slowly whisk in the flour until you have a nice, thick base.
Whisk in the milk. It won't be as thick as it will get in the end. Add the cream cheese - this is the real clincher for a perfect clam chowder! Peel (peel!!) potatoes and cut into bite-sized pieces. Add to the pan. Add in all other ingredients to the pan and stir. Make sure you also add all of the juice from the can of chopped clams.
Let simmer for about 18 minutes, stirring as needed. (If you don't stir it sometimes, you'll end up with a mess at the bottom and a harder time cleaning the pan!) I sit on a stool and read as I stir. Serve with oyster crackers.
Old Bay Seasoning can usually be found in your grocery seafood department or spice section. The taste before I added the cream cheese was right, but the consistency was off. No amount of flour or corn starch can make it right, but that half-block of cream cheese nailed it!