Combine the gelatin with 1/4 cup water in a small bowl or measuring cup and let stand for 3 minutes. In a small saucepan, over medium heat, combine 1/2 cup of the cream and the sugar. Cook, stirring, until the sugar has dissolved. Remove from heat and whisk in the gelatin. In a large bowl, combine the buttermilk, vanilla, and the remaining cream. Stir in the warm cream mixture. Lightly oil six 6-ounce ramekins. Divide the mixture evenly among the ramekins. Refrigerate, covered, 3 hours or overnight. To serve, run a knife around the edge of each ramekin and invert onto plates.