I made this on Monday and it was REALLY good. One caveat, though. My balsamic was syrupy to begin with - I think it's aged 20 years or something. Anyway, once it was reduced it turned gummy. So don't try this with the thicker balsamic vinegars! Otherwise, dinner was fabulous. I served the steak and onions with the potato-bleu cheese cakes and steamed broccoli. Mmmmmmmmmm.
"I will not defend my patriotism to those with the vile audiacity to have questioned it. A true patriot loves what his country stands for, not necessarily what his country does, and I will not shrink from holding America to her ideals." - Eric Zorn