Why do recipes call for unsalted butter, then tell you to add 1/2 tsp
of salt? Why not just use an appropriate amount of salted butter with
the unsalted?

In making these short breads, I find salt crystals that don't dissolve
in the batter, and don't want it. I've tried adding the salt when
mixing the sugar/butter and that helped, but still not perfect. I
could dissolve the salt in the vanilla, but don't want to do that.

I've found a very fine salt but it's expensive, (the amount would be
different) and I can't seem to crush my own fine enough.

Ideas?