Put the egg yolks and sugar in a mixing bowl and beat on medium speed until mixture is almost white and very fluffy, 3-5 minutes.
In a small saucepan, bring 1/2 cup heavy cream to boil.
Beating the egg yolk mixture continuously on low speed, pour in the hot cream in a thin stream until fully incorporated.
Briefly heat 2 tbsp grand marnier.
In another bowl, using clean beaters, whip the remaining cream at medium speed until it is firm enough to form stiff peaks that hold their shape when the beaters are lifted out.
Briefly beat in 2 tbsp more of the grand marnier.
Put the ladyfingers in a shallow bowl and drizzle them with the remaining grand marnier, leaving them to soak for several minutes.
With a rubber spatula, stir about a third of the whipped cream into the egg yolk mixture.
If you want to make the dessert look like a souffle, take a length of parchment paper, waxed paper, or aluminum paper about 2 inches longer than the circumference of a 1-quart souffle dish.
Fold the paper lengthwise in half and wrap it around the rim, rising about 3 inches above the rim, using freezer proof tape to tape it securely in place.
Spoon one-third of the mixture into the souffle dish (or loaf pan).
Arrange three of the ladyfingers evenly on top.
Top with another one-third of the mixture, then the remaining ladyfingers, and finally the remaining souffle mixture.
Put the dish or pan in the freezer and freeze for several hours, until the souffle is firm.
Remove from the freezer about 20 minutes before serving, to soften slightly at room temperature.
To serve, dip a serrated knife in hot water.
If using a souffle dish, remove the paper collar and cut horizontally even with the rim to free the top portion of the souffle and then cut it into wedges; continue serving the portion inside the dish by cutting wedges and carefully lifting them out with a cake slicer.
To serve from the loaf pan, dip the pan briefly in hot water, then unmold onto a platter and cut into slices.
Serve on chilled dessert plates, garnished if you like with candied orange peel and fresh berries.