This impressive and sumptuous special-occasion dessert, composed of two “go-to” recipes from Dominique Ansel’s book “Everyone Can Bake,” is easier to make than you might think. We did modify both his chocolate cake and the mascarpone whipped ganache, and we also added a coffee syrup for moistening the cake before assembly. We fold a chocolate-hazelnut spread (such as Nutella) into half of the whipped ganache to sandwich between the cake layers; the remaining whipped ganache is spread on top, creating a unique striped effect. The cake itself has the deepest, richest flavor and color when made with a good-quality dark Dutch-processed cocoa powder—we had the best results with Valrhona. Part of the beauty of this dessert is that the cake and filling can be made ahead; even after assembly, the dessert will hold nicely for up to 24 hours. We recommend making the ganache base and the cake a day in advance and refrigerating them separately. The following day, whip the ganache, assemble the dessert and refrigerate for at least two hours or for up to an entire day. For neat slices, cut the cake with a serrated knife that’s been warmed in hot water and wiped dry. To store leftovers, press plastic wrap directly against the cakes’ cut sides and refrigerate for up to two days.