I have noticed that there is still a lot of confusion whether handmade pottery is microwave safe. Sometimes all ceramics are considered unsuitable for use in the microwave.
But rest assured, your favorite handmade cup or plate can be absolutely suitable for the microwave, provided the ware does not absorb water(!). In addition, the piece should be finished with a suitable glaze for daily use. But that is always important, not only for microwave use.
So you can use handmade pottery as you like, even in the microwave.