Heat a skillet or a frying pan over medium-low heat. Place the coriander seeds on the pan. Toast, gently stirring, swirling, moving/shaking the skillet so the seeds are moving around to get toasted all around. Toast for no more than 2-5 minutes.
The seeds will darken a few shades in color and you'll start to smell the seeds. Allow the seeds to cool completely, then grind in a coffee grinder (dedicated to spices, aromas do transfer over). Pulse a few times to get a slightly coarse powder(basically not too fine powder). see image!
Notes
Exact toasting time depends on the moisture content of the seeds and quantity you’re toasting.
Grinding while hot can release natural oil, not great for storing.