Related: Why will Superheavy/Starship have a landing pad so close to the launch pad?
Most launch vehicles are launched from somewhat complex launchpads with towers, erectors, flame trenches or deflectors, water deluge sprays, the actual pads themselves, service structures, pipes that are connected to the rocket until the last moment, supports for the base of the rocket, etc.
SpaceX's current rocket lower stages land on a flat landing pad, but they launch from a launch pad with all the above amenities.
Has any rocket launched from a plain-old flat surface (whether or not a specially prepared one) into orbit? Has any detailed proposal, that wasn't a spaceplane, proposed doing this?