Traditional buns have a flat bottom where they rest on a baking tray. One solution to this problem would be to bake in outer space, another possible solution would be to develop a rapid baking process that allows baking in a free-fall aeroplane, but both of these would be unreasonably expensive.
It seems that it would be viable to bake double-ended buns by having a rapidly rising column of hot air to suspend the bun. The terminal velocity of a bun would probably not be that high (maybe 60Km/h) and it should be quite easy to have a pipe full of hot air that bakes the buns. As slight variations in the density and shape of the bun would affect the air-flow it would be necessary to closely monitor the process and adjust the air speed to keep the bun afloat. Manufacturing cheap ovens that use LASERs to monitor the position of the bun should not be difficult.
This might blow the sesame seeds off the bun, but this problem may also be solvable through careful design of the bun shape to make it less aerodynamic and by strongly attaching the seeds. I’m not sure how you would do this.