How to prevent separation/layers in panna cotta? I recently discovered how easy it is to make panna cotta via a recipe by Mark Bittman. The only problem I found was that my panna cotta started to visibly separate into two distinct layers after a couple hours in the fridge. Google searches brought up others that complained of different types of separation, but mine was, unlike most, very much gelled layers with one creamier than the other on top. I enjoyed the distinction between the two while eating, but I would like something more evenly distributed in the future.

I followed Bittman's directions to the letter, with the same proportions and quantity of everything but the lime that I substituted for dried lavender to taste. Half an hour or so of cooling time before pouring brought it down to room temp, which was ~65F. I strained, poured, and chilled for 5 hours before serving.

Is there anything I can change in the future, including the proportion or mixing of half-and-half and cream (which I suspect is the cause of separation), that would prevent this from happening? I would not mind leaning towards an all half-and-half solution to this, as the richness of all cream feels kind of cloying to me.
It sounds to me like you didn't get the gelatin dispersed properly.

Since the recipe you linked to doesn't explicitly mention it, and neither does your question, I'm going to assume that you didn't bloom the gelatin first.  You must do this if you want proper dispersion of any gelatin product.

To bloom powdered gelatin, just sprinkle it over cold liquid and leave it (cold) until it's visibly swelled. This usually takes about 5 minutes.  Then simply heat and stir (thoroughly) to disperse.

To bloom sheet gelatin, you do almost the same thing - soak them for a little longer (up to 10 minutes) in cold water a separate vessel, then squeeze them to wring out any excess water, and then add to your cooking liquid (in this case cream).

You might also consider use a stick blender/immersion blender to make sure that it is completely dispersed after melting. This is usually unnecessary for gelatin, but if you're blooming it and still can't get uniform distribution, that will help.

I'm certain that if you follow the proper preparation, your panna cotta will turn out fine next time.

P.S. Do be careful not to add too much lime or other acid; gelatin will not set properly at pH levels around or below 4.