Caramel Sauce

Has anyone else tried this recipe? I followed the instructions to a "T", but as the sugar/water mixture boiled the sugar formed a crystallized crust on the surface, preventing me from seeing what was happening underneath. I tried to use the color between the cracks as an indication of when to remove it, but when I finally did (and I did not dare stir it in the meantime) it had already hardened into a solid disk in the bottom of the saucepan. I added the butter and milk hoping the sugar would re-liquefy, but I'm afraid I may be resigned to chipping it out with a jackhammer. Until I find out exactly what went wrong, I won't be trying this again.

This recipe tastes great and is good for drizzling on ice cream. But, it is rather thin. I needed a good thick caramel sauce for another recipe and this was too runny.