>Problem is that I can't get my challah to be as soft as I would like it;
>I've baked at temperatures ranging from 230-250C or 450-500F (although my
>oven can get up to 290C).
Your baking temperature is high for Challah, my standard Challah (Reinhart
BBA) is baked at 190 C or 180 if I'm baking a large celebration loaf. The
crust is crisp when it comes out of the oven but softens later. Try
reducing the temperature and upping bake time by about 10% before you start
testing for the loaves being cooked.
John