Combine Grand Marnier with Simple Syrup; set aside.
Use a serrated knife to cut the Génoise, horizontally, into 3 layers. Place the top layer upside down on the cake circle. With a pastry brush, moisten it with some of Grand Marnier syrup. Spread half the apricot jam over moistened cake layer. Spread ⅓ cup Chocolate Buttercream evenly over jam. Brush the second