Moving heat problem: instant toast?

Question

Toast-making usually takes a couple minutes using something like a conventional toaster oven to brown the surface of a piece of bread, making toast. However, this duration may be inconvenient. What methods of non-destructively toasting bread could accomplish the task 'instantly'? Instantly can be from infinitesimal time to about 5 seconds, to be on par with the time it would take to get the bread out in the first place.

Possible options:

• At 1 second 'instant', radiant heat from a hot (electric) element could still be practical
• At sub-millisecond 'instant', a flashbulb of sufficient intensity could heat the surface of the bread, but would this be able to actually cause toast?
• Nuclear weapon options seem more likely to need kilometers of separation between the bread and the source, making it inconvenient to have heated the bread and a new nuclear wasteland
• Superheated steam seems like an option, since it can be very hot and has a high heat capacity, though I have no idea what time scale would be appropriate for it

Answer 1

Toasting not only browns the surface, it dries out and cooks the interior. Any method that applies heat to the surface and waits for it to diffuse into the interior is limited by the rate of diffusion. You can speed it up by a higher surface temperature, but this leads to uneven cooking.

Radiation and particles can penetrate to the interior, and can be switched off quickly. However, once the interior is hot, it takes time to cool off. If you heat enough to cook quickly, you may overcook by the time it cools.