Pour your batter into the custard cups and place the cups in a deep pan. Pour boiling water in the pan until it reaches halfway up the cups. Cover your cups with tin foil and bake for 30 minutes. Turn off your oven, leaving the cups inside, and let stand for 20 minutes. Remove the cups from the oven, uncover, and let cool completely. Cover your cups with plastic wrap and let chill in the refrigerator.