I love meringue mushrooms. I've been making them to garnish my annual bûche de noël, or Yule log, since I was a little kid, and my love for them has only deepened over time. Slowly, they've transformed from the clumsily assembled, hyper-sweet, Styrofoam-like sugar puffs of my childhood to something a bit more flavorful and sophisticated but every bit as fun.
Traditional meringue mushrooms start with a hard meringue, one that's made with more sugar than egg whites, and for that, I like to fall back on my basic Swiss meringue. Because it's fully cooked on the stovetop, it pipes true to form when baked at low heat, so I don't have to wonder how my meringue caps and stems may inflate or deform as they bake. What I pipe is what I'll get, so from the very start I know how my mushrooms will look in the end.
While meringue mushrooms are most often used as a garnish, with the actual dessert experience coming from the Yule log itself, I like mine to have enough flavor to stand on their own. To that end, I use toasted sugar to lend some caramel notes to the meringue and bring its sweetness down a notch. A pinch of salt and cream of tartar help round out its flavor as well, along with a generous splash of vanilla extract (which can be adjusted to taste).
For even more flavor, I buff the finished meringues with a high-fat cocoa powder (while I prefer the darker flavor and color of Dutch, natural cocoa powder works just as well). Finally, I glue the caps and stems together with some top-notch chocolate.
The brand and style of the chocolate hardly matter so long as you love its flavor, but dark chocolates in the 70% range tend to be easiest for beginners to temper (see our guide to the best supermarket dark chocolate bars for some suggestions on brand). That said, milk chocolates rich in cocoa butter are a solid option as well, so long as they don't contain any added palm oil (all of our favorite supermarket milk chocolate bars do nicely in this context).
With so many good ingredients involved in their making, these meringue mushrooms can't help but be a treat of their own, making them so much more than a cute garnish. Just don't expect to be wowed by the flavor of those made with white sugar; rubbed in starchy, low-fat cocoa; and pasted together with cheap chips. Recipes as simple as this can't be better than the sum of their parts.
I've covered how to make Swiss meringue pretty extensively in the past, so I'm going to jump straight into the mushroom-making technique.
I start by dividing the meringue between two disposable pastry bags, one fitted with a 1/2-inch round tip and the other with a 1/4-inch round tip. This makes it easy to pipe mushroom caps and stems both large and small, wide and skinny, thick and thin, for a more diverse arrangement in the end.*
*It will be hard to resist cracking a few sophomoric jokes as you pipe the stems, but their questionable appearance will resolve when the mushrooms are assembled later on.
To pipe the caps, I hold the bag perpendicular to a parchment-lined half-sheet pan, with the tip about 1/4- to 1/2-inch above the surface. By squeezing on the bag without raising the tip, I can pipe a wide, flat disc like the cap of a shiitake. By slowly raising the tip about 1/2-inch as I pipe, I can create a more rounded, button mushroom–like shape. By continually raising the bag as I pipe, I can create the stems.
The biggest trick is to stop squeezing the bag before moving the tip away when you're done, so the meringue doesn't continue to flow out in a trail; otherwise, the process is fairly intuitive and easy to figure out on the fly. Plus, the recipe intentionally creates a little excess meringue so you can comfortably experiment with different piping styles. This leaves plenty of room to practice and learn. And crack jokes. And make questionable Instagram videos (as the entire Serious Eats team gathered to do when I was piping this batch).
After the caps and stems have been piped, any exaggerated peaks or deformities can be smoothed away with a wet fingertip (just dip your index finger in a dish of water between each one). Smoothing and molding the caps with water can create wrinkles and folds in the meringue as well as water spots, and while these might be "defects" on a fancy meringue cookie or macaron, they only make these "mushrooms" look more natural and organic.
See what I mean? But I'm getting ahead of myself. Before the meringues can look like mushrooms, they have to be baked.
When they go into the oven, the meringues will look glossy and wet, with a bright white-to-ivory hue (depending on how darkly the sugar was toasted). But after a long stint in a low oven (about three hours at 225°F, although the timing can vary depending on the size, shape, and quantity), they'll turn a matte beige and feel firm and dry to the touch. Once baked, I cool the meringues to room temperature in the oven itself, with the door tightly closed, letting them further dry as they cool.
The timing of the cooling phase can vary a lot from oven to oven (some retain heat better than others, some have a venting system, some have a poor seal on the door), but it takes about four hours for me; long enough that I generally like to save this project for later in the afternoon, so I can let the meringues cool overnight. Otherwise, the baking and cooling phase can end up occupying my oven for the better part of the day, which isn't ideal during the holidays.
Once the meringues cool and dry, I dust them with a high-fat cocoa. I've found the mushrooms tend to look more realistic when the caps are darker than the stems, so I go heavier on the former than the latter, but that's mostly a matter of personal taste.
Next, I rub that cocoa into the surface of the meringue, buffing the caps and stems until they're a mottled brown all over. If needed, I may dust with more cocoa to get a deeper color here and there. It's a little messy, but truly hard to go wrong; the more smudged and "dirty" the mushrooms look, the better.
At this point, the meringues can be used right away for assembly or stored for up to a week before final assembly (wrap them tightly in plastic or transfer them to an airtight container). The cocoa dusting keeps the pieces from sticking together, so they can be jumbled together in a bag without any fuss.
Before assembling the mushrooms, however, I like to sort through the pieces, mixing and matching caps and stems to find the size and shape combinations that look best to my eye.
I find something about the process incredibly soothing, like working on a puzzle, but don't fuss over it too much if you're not as enthralled. The mushrooms tend to look cute no matter how they're put together.
To assemble the mushrooms, you'll need to temper a little chocolate; it might seem like a pain, but if the chocolate is simply melted, rather than tempered, it won't set up nicely at room temperature, so the mushrooms will have to be stored in the fridge and served cold (gross). The melted chocolate may also develop a mealy consistency over time (also gross).
Once tempered, spread a little chocolate over the bottom of a mushroom cap, then dip the very tip of a mushroom stem into the chocolate as well, and join the pieces together, with a gentle twist to secure the cap and stem together—it's more about balancing the pieces together in the thick chocolate than achieving a snug fit. Arrange the assembled mushroom upside down on the empty baking sheet, pressing the stem firmly into the cap if it seems unstable.
If a stem seems especially precarious, it can be propped up against the rim of the baking sheet, or a neighboring mushroom. Don't worry about stems that lean or shift a little, they'll look great when flipped back over, but do fix any stems that fall over altogether.
Once the mushrooms are upright again, you may want to dust them in a bit more cocoa powder, so they look as if they've freshly emerged from a patch of soft earth. The finished mushrooms can be stored in an airtight container for another week or used right away, but do keep them stored until the last minute. They're likely to soften when left out in a humid kitchen environment.
Whatever recipe you use for the Yule log itself, these meringue mushrooms will make a worthy garnish, lending both charm and flavor to this iconic, Christmas dessert.