A few smart moves make this Bûche de Noël a cut above the rest. Allowing the cake to cool while still rolled helps prevent cracking. Mascarpone stabilizes the whipped cream filling so that it can chilled up to overnight without weeping. Butter and corn syrup in the ganache keep it smooth and glossy. And stirring slivered toasted almonds into the ganache frosting gives it a “tree bark” look and adds contrasting texture to the silky filling and tender cake.If you’d like to make Meringue Mushrooms to decorate the cake, feel free to bake them up to 3 days ahead.