Whisk egg yolks and 7 tablespoons sugar in medium bowl until thick and pale yellow, about 2 minutes.
Bring cream to a simmer in heavy small saucepan.
Gradually whisk hot cream into yolk mixture.
Whisk in Grand Marnier and vanilla; divide custard among six 3/4-cup custard cups.
Arrange cups in 13x9x2-inch metal pan. Pour enough hot water into pan to come halfway up sides of cups.
Bake custards until gently set in center, about 25 minutes.
Remove cups from water and refrigerate uncovered until cold, at least 3 hours. (Can be made 1 day ahead. Cover and keep chilled.)
Preheat broiler. Place custards on baking sheet. Sprinkle 1/2 tablespoon brown sugar onto each. Broil until sugar starts to bubble and color, turning sheet often to prevent burning, about 2 minutes. Chill until topping is hard and brittle, at least 1 hour and up to 6 hours.