Add a little sugar.

Seconding Senyar: start by adding a little sugar and see if it helps.

If you do decide to add baking soda, start with just a little and see how it goes. I use it in cream of tomato soup, but in other dishes, I sometimes find that adding enough soda to make a difference leaves the soup tasting and feeling a little bit soapy.

Or what about serving it with a swirl of sour cream or yogurt or cream to balance the tartness? Would that do the trick?

yeah, sugar or cream always do it for me.

Sugar helped; I probably added a Tbsp. or so. Thanks for the suggestion, Senyar & Elsa. I also tried a sprinkle of soda over a spoonful; that didn't seem to make much difference so I've abandoned the idea.

Now that I think about it, I can recall reading something molecular-gastronomy oriented, wherein the author was discussing the chemistry of taste, and noted that "Adding sugar to something sour doesn't change the number of hydrogen ions in the solution, but it does not taste as sharp."

What might mellow it out also are some starchier ingredients. Do you have a can of hominy around?

Yeah, frozen corn might help. I often toss in some corn if thing start tasting too sharp.

I think sugar was your best option. You can add some Marsala wine if you have any handy, as well.