If you don't cook with rosemary that often, you probably just have some dried rosemary in your pantry for those rare occasions a recipe calls for it.
Or maybe that's just me, but I use it in such small quantities here and there that I never use up all the fresh rosemary I would buy, and I can only infuse so many bottles of olive oil with leftovers!
Unfortunately, dried rosemary is immensely prickly, and you can't chop it up the way you can with fresh (tho frankly even fresh rosemary is quite prickly!) so you probably end up with spiky twigs in your finished dish.
Here is my forehead-slapping-ly obvious solution:
The good ol' Mortar & Pestle.
Place however much dried rosemary you need at the bottom, and add a pinch of kosher or sea salt (not table salt, as that is too fine to assist in breaking down the rosemary.)
Give it about a minute or so of really solid grounding, rubbing it against the sides as if stirring vigorously.
There may be a few stubborn twigs left (probably stems anyway) but you should be left with an only slightly coarse yet pungent powder that will dissolve nicely into gravy, or that you can use to stuff a roll of pork, chicken, or lamb, and not worry about anyone getting stabbed in the tongue.
It seems obvious, but if you don't use your mortar and pestle that often, you can forget that you have one!