・Soak the prunes in rum for about 5 hours. ・Arrange the soaked prunes in a buttered gratin dish. ・In a bowl, combine all ingredients except the prunes and stir gently until incorporated. ・Pour the batter into the gratin dish. ・Bake for 55 minutes at 190C degrees. After 20 minutes put the remaining prunes on top and keep on baking. ・Serve it while warm. If it’s completely cooled, warm in the microwave for 30 seconds. ・Sprinkle powdered sugar if desired.