Thursday is Koopers Day at City Paper, The Sun, the Transit Administration, and elsewhere along N. Calvert Street. Been that way for ages. The tan and brown Chowhound truck is adorned with a picture of Cooper, the friendly looking dog who, before his death, served as the brand's mascot. The truck posts up next to the parking garage, its chimney wafting a magic burger smoke. The $11 burger is a luxury, both in cash and calorie, but they do it so right. You ask for medium rare, and you get a medium-rare, 1/3-lb patty. There's "Elvis Got The Blues" with bleu cheese and bacon; and Gonzo sliders, two smaller burgers infused with Flying Dog Gonzo Imperial Porter, celery, and mushrooms and topped with cheddar cheese, caramelized onion, tomato, and a bit of jalapeno heat. Lately, if we don't get the MacGuinness (black angus beef, bacon, and cheddar) or a full custom job (you can choose from roasted red peppers, truffle arugula, feta cheese, Baja slaw, chipotle mayo, and 25 other toppers) we go for one of the newer chef specials, which carry a little heat and a little sweet.