Recipes are lists of ingredients; technique is what turns good recipes into great dishes. And in the course of all of that panna cotta testing, I found a couple of little tricks that are really important, because there is little more disappointing than thinking you've perfected a recipe only to have it flop.
On two occasions, panna cotta recipes that had previously worked failed. I unmolded the ramekins to find that somehow the mixture had separated into a thin layer of clear gel at the bottom and a stiff custard on top. It's not an uncommon problem.
There are two easy steps to prevent it. First, before you take the pan from the heat, rub a little bit of the cream mixture between your fingers — there shouldn't be any grit from undissolved sugar or gelatin. Then whisk the mixture in an ice bath until it's lukewarm.