I usually make a dessert with pastry cream for Christmas and thought it would be interesting in a Bûche. I'm guessing a biscuit dough would be something like this, at joy of baking or this, at baking 911? I just found the Baking911.com recipe, it specifically calls for a pastry cream filling with a sponge base and buttercream icing. Which is exactly on target for what I was planning. Although I plan to use a meringue, Italian instead of a whole-egg buttercream.