The onion burger at Duke's Old Fashioned Onion Burgers features a thin beef patty smashed on the griddle with a pile of sliced onions, creating a crust where the meat and onions fuse together, then finished with cheese and served on a soft bun.[3] This style, inspired by Oklahoma onion burgers, delivers a distinctive flavor where caramelized onions are integrated directly into the patty rather than acting as a topping.[3] The eating experience centers on the contrast between the crisp edges of the patty, the sweet browned onions, and the squishy bun, yielding a burger that feels both simple and very specific in character.[3] Burger-focused video coverage notes how the hand-cut fries and shakes complement this signature burger, framing the spot as dedicated to this one particular style.[3][6]