Was traveling solo on business on Valentine's Day so getting any sort of reservation was going to…read morebe difficult at best. Came across this sit down gourmet burger place (focusing on all natural ingredients) just north of Frankfurt Süd S-Bahn train station. Apparently this is a high end burger chain that was started (and is mostly based) in NYC.
The service was good, and the menu was nicely laid out with explanations in both German and English. I was rather hungry and wasn't planning on having dessert, I had two sides of panko coated chicken tenders (with two dipping sauces) and fried Brussels sprouts w/ (duck) bacon and shaved Parmesan. For my burger I had the Blu Moo (duck bacon, blue cheese and sautéed mushrooms on a beef patty on a whole wheat bun). For a drink I stuck with a peach iced tea (unsweetened and free refills!)
All the food was great and tasty. And at the end, found that they didn't just take credit cards, but was able to use my corporate AmEx card (which is still somewhat a rarity in anything other than high end restaurants in Germany). The prices are expensive (it all ran around $52) but the sides would easily feed two, and some of it is justified by the sustainable ingredients that they use.