*I can't stress the importance of using a heavy pan. Thin pans do not distribute heat well and can easily burn a sugary mixture like this.
*It's important to let the mixture cool before storing. If you cover it too soon, the steam from the warmth of the mixture will condense, drip back into the mixture and cause graininess.
*If it does get grainy while being stored in the refrigerator, there's no need to fret. Just measure out however much you're going to use, add a splash or so of heavy cream, stir it up and reheat in the microwave. The grains should melt right back into the mixture and it will become smooth and glossy once again. If it's still grainy, just add a bit more cream and heat again for a few seconds until it's smooth. You can also add a teaspoon of corn syrup to the mixture to help retard any further crystallization and help with some of the chewiness.
*The sauce keeps in the refrigerator, covered for about a month. I just scoop out whatever I'm going to use and heat it up (I let it just start to get bubbly) with some cream (and maybe a little corn syrup) and I am good to go! Recipe from Gourmet Magazine, June 1993