There are all kinds of ways to do a yule log, this is just one of scores of possible directions. So, take the below as a general guide and improvise as you see fit. I’ll try to point out opportunities for variation along the way.
Actually, here’s one right off the bat. There’s a school of thought that holds that buttercream is too rich a filling for a cake as decadent as a bûche, and I can sort of see the point. So if you prefer, leave out the coffee-flavored buttercream and substitute a generous brushing of coffee-flavored cake syrup. If you decide to press on with the buttercream, apply only a thin layer to the unrolled génoise.
…except for right here at the far end where the roll begins. Apply a long mound of filling there, about an inch high, about two inches in from the very edge of the cake sheet. That gives the cake a center to roll around, and keeps the innermost part of the roll from breaking. See here I’m just filling up the little crook in the cake that remained after I unrolled the cooled sheet. Looks messy now, but trust me, it’ll turn out just fine.
Now gently roll it back up.
Lay the cake on a cutting board with the seam to the side, just touching the board.
For the side branch, you really don’t need to cut too much of the cake off. See there on the right? I’m not taking even two inches off that side of the roll. Keep the seam on the long side of the cut, as that will help keep the branch piece from unrolling as you’re working with it.
See what I mean about that cream-filled center? Looks nice.
Figure out about where you want to place the branch. Some people like to put it on the top, sticking up. That’s always seemed a little dangerous for me. I like the side presentation. I should insert here that in some yule log-making traditions, a piece is never removed from the end. Small mounds of buttercream are place here and there along the length, and the ganache “bark” is simply piped around it. It’s a good method, though I avoid piping where I can…
…for obvious reasons. Yuck. Oh well, it came out good enough. I should have applied more pressure to the bag (I wouldn’t have gotten those rough edges). But heck, it’s fine. Use a medium-to-large star tip for this bit, as it creates the impression of wood grain. Doing the ends — or at least two of them — with the pieces upright is helpful. Have someone hold the trunk piece while you pipe (if possible).
Place the cake on a platter or board of your choice. Now’s a good time to brush off a little of that extra flour if you can. Then get out the ganache. You’ll have to fill in that gap where the branch meets the trunk, which isn’t difficult. Room-temperature ganache is very forgiving. You can apply it and re-apply it almost endlessly.
This is the bark effect I like. Lots of folks like to use a fork to make deep lines in the ganache along the length of the log. If that’s you, go nuts! The nice thing is that if you don’t like it, you can just smooth it all out again and start over. To get those little bark “points” that stick out over the edges, just continue your stroke out over the edge of the buttercream. A little of the ganache should come with you.
Now for the mushrooms. I dust mine with a little cocoa powder to give them a textured look. Pastry chef Laura mentioned that you can apply cocoa powder before you even bake the mushroom tops. I’d never heard of that, but it sounds like a great idea. Next year I’ll try it.
Now all you need to do is stick the mushrooms wherever you want. I do mine in clusters, as I mentioned. I like the look, what can I say? Someone recently told me that ground up pistachios make great moss. That’s something else I’ll have to try next year.
Now all that’s left are the marzipan holly leaves. They’re very simple. Just roll out a small piece of marzipan — which you kneaded green food coloring into, obviously — on a board that’s been lightly dusted with powdered sugar. Use a small cutter to nip away bits of the edge and create those spiky leaves. Here I’m using the smallest cutter from my Ateco set.
Arrange them as you wish with a few red red marzipan berries and you’re pretty much good to go! Oh, a little powdered sugar “snow” dusted on top makes a nice finish, but it’s completely your call. Wipe any errant bits of ganache or buttercream off your platter and you’re finshed! A yule log will keep well in the refrigerator, unwrapped, for up to two days.