Preheat oven to 325 degrees. Into a 13 x 9 metal baking pan, pour 3 1/2 cups hot tap water. Place in oven.
In 2 cup glass liquid measuring cup heat creams on medium power in microwave for 5 minutes. Remove from microwave and stir in vanilla.
Meanwhile in a 4 cup liquid measuring cup or bowl, whisk egg yolks and granulated sugar until well blended. Slowly whisk in warm cream until combined. Skim off foam with spoon.
Partially pull out oven rack with baking pan. Place 6 ceramic of glass (4 oz) ramekins in water pan. Pour cream mixture into ramekins. (Mixture should come almost to tops of ramekins for successfull broiling later.) Carefully push in rack and bake 30 minutes or until just set but centers jiggle slightly. Remove ramekins from water and place on wire rack, cool for 30 minutes. Cover and refrigerate until well chilled-4 hours or overnight
Up to 1 hour before serving, preheat broiler. Place brown sugar in coarse sieve, with spoon press brown sugar thru sieve to evenly cover tops of custard. Place ramekins on jelly roll pan for easy handling. Have broiler rack at the closest position to heat. Broil 2 to 3 minutes or until brown sugar melts. Refrigerate immediately 1 hour to cool custards and to allow sugar to make a crust. Serve.