Mix the eggs, milk, and flour, then add the vanilla sugar, melted butter, and Grand Marnier.

To make the soufflé mixture: Whisk the egg yolks with the sugar until pale, add the flour, then the hot milk. Return to the saucepan and cook over low heat until thickened. Off the heat, stir in the Grand Marnier and let cool completely at room temperature.

Preheat the oven to 350°F (180°C).

Once the cream has cooled, beat the egg whites until stiff peaks form and gently fold them into the cooled mixture.

Spread a crêpe on a silicone mat or parchment paper, add 2 tablespoons of the soufflé mixture to one side, then fold the other side over.

Bake for 5 to 6 minutes. Serve hot, dusted with powdered sugar.