I used to have a furnace at 815 degrees C for lab testing. Tried a toasted ham and cheese sandwich in it once, got charred bread and unmelted cheese in the middle.
Basically the heat flux is so much that you can't transfer it through the food fast enough to cook the inside before the outside burns. Which is why you can't turn up your oven to twice the temperature and cook your food in half the time.
This needs to be a sign in my works cafe as I've had guys look straight and me like I kicked their dog because the conveyor belt toaster isnt at 11. I'm sorry I don't like burnt cold bagels...
I get that it’s the onion, but I will add that if you tried to heat anything in a cremation oven it’d be gone. Those things run at 2k+ degrees. So the cup and coffee would be legit vaporized.
Nah, water wouldn't vaporize instantly, it takes a while. But the mug would definetly crack from thermal shock. Unless it would be a metal mug in which case it might work. The coffee would probably be boiling in seconds.
Camp fire mug would do it but it would boil out the contents in a moment from the near instantly achieved rapid boil. And not fully evaporated just nuked into steam as it ejects / "explodes" from the cup. Would look a lot more violent then rapid nucleation.