It separated into two distinct layers just as fat separates from water. The top layer was rich and fatty and the bottom layer was noticably lower fat. Never had this happen before.
The recipe was from Edward Giobbi and Eugenia Bone's Italian Family Dining. Unlike other panna cottas I have made, this recipe instructed you to cook the cream, milk, sugar, vanilla and dissolved gelatin "over medium-low heat for about 10 minutes..... until the mixture is just about to boil." Could the high heat do it? Should I try stirring as it cools or would that mess up the gelatinization?
BTW, it was delicious anyway with a layer of gelled pureed strawberries.