Makes enough ganache for one 4-layer 9-inch cake
Place chopped chocolates in a large heatproof bowl and set aside.
In a small saucepan, combine cream, sugar, and Grand Marnier, and bring just to a boil. Immediately pour cream over chopped chocolates and allow to sit, undisturbed, for 5 minutes, then whisk until smooth and thoroughly melted.
Set aside to cool to room temperature, whisking or stirring occasionally to facilitate even cooling. Use to frost Triple-Chocolate Cake as instructed.