We did go to Mercat a la Planxa, and it worked out great. To get to the Loop, I took the Blue Line from Cumberland to Jackson, then met up with my friend at her office, 600 S. Michigan. The restaurant is at 638 S. Michigan, and here's a location tip: The entrance is inside the Renaissance Hotel. I don't recall signage at street level; KT just happened to remember from a previous visit.
Oh, another tip, from a safety perspective: Change your prescription sunglasses for regular lenses before navigating the steps to the restaurant so you may avoid tripping "up" the stairs and appearing less than graceful ...
Anyway, the food! As mentioned upthread, the $18 Catalan Express lunch menu offered lots of tasty-sounding options. You choose two courses; because it is a tapas restaurant, I was assuming portions would be small, but that was most certainly not the case here. The lunch deal also includes a fountain drink or iced tea; be forewarned that they serve Pepsi products! Their tea was good; nothing fancy or flavored, just straight-up and fresh-brewed.
For the first course, KT opted for the salad featuring Serrano ham and figs over spinach with a sherry vinaigrette, and pronounced it very good. I can't provide any other nuances, but she did not leave anything on her plate and did not offer me a bite!
I had the gazpacho; their version was tomato and watermelon. It was light, refreshing and quite pleasing on the palate. Serving temperature was just right; not so chilled that you couldn't taste the flavor. It was accompanied by a a toast crisp topped with a crab-and-goat cheese mixture. I would most definitely order this again! I couldn't finish the bowl of soup, though; there was just too much of it, even though I really liked it.
We both ended up ordering the same thing for our second course -- hangar steak -- which is described as being prepared with "Potato Croquette, Braised Short Ribs & Beech Mushroom Escabeche." It was very flavorful, and grilled to medium rare as requested, but seeing that description now, I don't think the short ribs were definitive enough to add to the dish; at least, I can't remember tasting them as a component. I'm also unclear as to what Mercat means by "escabeche," since that would usually indicate something prepared in an acid-based marinade, and that was not the case here. In fact, if anything, the dish trended toward having an "oily" (not greasy) vs. acidic profile. I didn't ask our server about it, though, so this may remain a mystery!
All in all, recommended; I would definitely return.
Mercat a la Planxa
638 S. Michigan Ave.
Chicago, IL
(Inside Renaissance Hotel)
http://mercatchicago.com/
"When I'm born I'm a Tar Heel bred, and when I die I'm a Tar Heel dead."