I’ve done this one before- but it’s been awhile so just as a fun fact for anyone who doesn’t know:
If your food is cold and the container is hot you are using the wrong container for the food. The first thing to consider is wether the material of the dish reflects microwaves or allows them to pass through. If microwaves can’t easily pass through the dish- you’ll get poorer results. A dish that leaves as much of the food exposed as possible with minimal excess- a plate instead of bowl where practical, a bowl with lower walls, etc. but the material is very important.
Microwaves also use dielectric heating- they’ll heat things more readily that have polar molecules. If you want your food to be hotter than the dish- you have to choose the right dish. Borosilicate Glass is a decent microwaveable material. Other engineered materials and ceramics work well too- but not ALL ceramics. Some are very poor for the purpose as are many polymers.
If your food is cold and the container is hot you are using the wrong container for the food. The first thing to consider is wether the material of the dish reflects microwaves or allows them to pass through. If microwaves can’t easily pass through the dish- you’ll get poorer results. A dish that leaves as much of the food exposed as possible with minimal excess- a plate instead of bowl where practical, a bowl with lower walls, etc. but the material is very important.