This vegetable "condiment" was introduced to me by one of colleagues, Ian Halbwachs. He roasted the vegetables until they became like what you would find at the bottom of roasting pan with a large cut of meat, almost candied. To me, they give the burger a slight roast beef quality. I stir in some chopped pickles, pickle juice and ketchup and add a cheese sauce to give it a fancy diner vibe.