Step 1Pour the cold water into a small cup and stir in the gelatin. Let it stand for 5 minutes. It will become firm.
Step 2Place the milk, cream, salt and sugar in a small saucepan. Turn the heat to medium and stir often. Heat the mixture until a small ring of bubbles appears around the inside edge of the pan. You need to stand right there and watch carefully. This process takes only a couple of minutes, and sometimes you will notice a little steam rising from the milk mixture. Don't let it boil.
Step 3Remove the pan from the heat. Add the gelatin mixture and vanilla, and stir until the gelatin completely dissolves. Pour the custard into serving cups. I like to use 1-cup glass containers; each holds 2/3 cup custard. Let the custard cool a little, then cover each cup with plastic wrap and refrigerate 4 to 6 hours before unmolding to serve.