1/2 cup plus 1/3 cup sugar
1 cup milk
1 cup half-and-half
1 tsp. vanilla extract or 1 vanilla bean split lengthwise
4 large eggs
1. Preheat the oven to 300°F with the rack in the center. Grease 6 custard cups with neutral tasting vegetable oil.
2. Place 1/2 of the sugar in a saucepan set over low heat. Using a pastry brush, drizzle in 1/4 cup water down the sides of the pan. Do not stir the sugar. Cook until sugar turns medium-brown color. Immediately spoon 1 tablespoon of caramel into each custard cup. Set aside to harden.
3. In a small saucepan combine milk and half-and-half and heat over medium heat, but do not boil. Add vanilla extract or bean and remove from heat.
4. In a bowl whisk together remaining 1/3 cup sugar and eggs. Whisk 1 cup hot milk mixture into eggs to warm them, then whisk egg mixture back into saucepan. Remove vanilla bean, if used.
5. Pour mixture into custard cups, almost filling each cup. Place custard cups in a baking pan or small roasting pan. Pour warm water into pan to reach halfway up sides of custard cups. Bake for 20 to 40 minutes, or until custard no longer jiggles in center. Remove custard cups from pan to cool to room temperature, then refrigerate.
6. To serve, run wet knife around inside edge of cup. Place serving plate over custard cup and invert. Shake until flan separates from cup.