Heat oven 300F. Place a cloth napkin over the bottom of a roasting pan. Place 4 (5-inch) brulee dishes or 6 ( 6 oz) ramekins in the roasting pan leaving space between each dish.
Boil water in a tea kettle or a pan with a spout.
In a saucepan, bring the heavy cream and light cream just to a simmer. (you should see whisps of steam).
In a medium bowl, whisk eggs, ¼ cup sugar, salt and vanilla. While gently whisking, very slowly pour hot cream mixture into the egg mixture until combined.
Strain mixture into a large measuring up or bowl with a spout. Divide mixture evenly among brûlée dishes or ramekins. Place in prepared pan.
Pour hot water into roasting pan until it comes up half way the sides of the dishes.
Bake 25 to 35 minutes or until custards are set but still quiver in center.
Remove from water bath and cool. Chill in the refrigerator for at least 2 hours.
Can be made 2 or 3 days in advance at this point.
Just before serving sprinkle tops evenly with remaining sugar.