https://m.media-amazon.com/images/I/81Yd1s4GViL._AC_SL1500_.jpg

This is known as "memo pad tray". You find it at office supplies
However, you can use it as a make-shift Esbit stove

You could use it as is or make some mods.
For example, make holes in the bottom sheet, and four screws near the corners (as legs) to lift it a bit for better aeriation. or dent it downward to allow for some alcohol gel with the esbit cube. Or simply add a metal jar cap to contain the alcohol gel.

Please make sure there are no plastic or rubber components in it.
And pre-burn it a few times before using it for you cup of coffee.