Gluten-Free Mocha Yule Log

Preparation

1. To prepare cake: Preheat oven to 350°F. Line the bottom of a large (12-by-16 1/2-inch) rimmed baking sheet (half sheet pan) with parchment paper; coat the paper and pan sides with cooking spray. Place eggs (in the shell) in a stand mixer bowl or large mixing bowl, add very warm tap water and set aside to warm the eggs and bowl.
2. Melt butter in a small saucepan over medium-low heat, swirling occasionally, until the white flecks of milk solids in the bottom of the pan start to turn golden brown, 4 to 8 minutes. Scrape into a medium bowl. Let cool to room temperature, then add 2 teaspoons vanilla. Set aside.
3. Meanwhile, whisk gluten-free all-purpose baking flour (or baking blend) and 1/4 cup cocoa in a medium bowl; set aside.
4. Drain the water and break the eggs into the warmed mixing bowl. Add sugar and 1/2 teaspoon salt and beat with an electric mixer on medium-high speed until thick and pale light yellow, 5 to 15 minutes (depending on the power of your mixer). To test if it’s beaten well enough, lift the beater from the batter: as the batter falls off the beater into the bowl, it should mound for a moment on the surface.
5. Gently fold the flour mixture into the egg mixture with a whisk, in two additions, until just incorporated. Gently fold about 1 cup of the batter into the reserved butter. Then gently fold the butter mixture into the bowl of batter with a whisk until just incorporated, being careful not to overmix. Spread the batter evenly in the prepared baking sheet, spreading completely to the sides.
6. Bake the cake until puffed and a toothpick inserted in the center comes out with a few moist crumbs attached, 8 to 12 minutes. Cool in the pan on a large wire rack for 10 minutes. Gently run a knife around the edges and turn the cake out onto the rack; remove the parchment and let cool completely. Once cool, cover with 2 overlapping pieces of plastic wrap and a clean, damp kitchen towel to prevent it from drying out. (The cake can be held this way for up to 4 hours before assembling the Yule Log.)
7. To prepare filling & frosting: Bring 2 inches of water to a simmer in the bottom of a double boiler. (No double boiler? See Tips.) Combine agave nectar, instant coffee, reconstituted egg whites, cream of tartar and 1/4 teaspoon salt in the top of the double boiler. Beat with an electric mixer on medium speed until well combined, about 1 minute. Place over the simmering water and beat on high speed until the frosting is glossy and has the texture of very thick shaving cream, 5 to 10 minutes. Remove from the heat and beat in 1 teaspoon vanilla until just combined.
8. Leaving the towel and plastic wrap over the cake, invert it onto a work surface with a long edge nearest you. The towel will now be on the bottom, with the plastic wrap directly beneath the cake. Combine coffee and half-and-half in a small bowl. Brush the top of the cake with the coffee mixture; let it soak in and continue brushing on more until all of it is absorbed.
9. Spread about two-thirds of the frosting evenly over the cake. Using the plastic wrap, lift the long edge and roll the cake into a log lengthwise. Cut a 3 to 4-inch “branch” off one end at an angle. Place the longer log on a serving platter, seam-side down. Use a little frosting to attach the branch to the main log. Cover the cake and branch with the remaining frosting. Make decorative ridges in the frosting with a fork to resemble bark. Let the cake stand at room temperature for at least 30 minutes or up to 2 hours. Or refrigerate, uncovered, for up to 1 day.
10. Just before serving, garnish the serving platter with Sugared Rosemary and Meringue Mushrooms, if desired.

Tips & Notes

• Make Ahead Tip: Prepare through Step 9 and hold at room temperature for up to 2 hours or refrigerate, uncovered, for up to 1 day. | Equipment: 12-by-16 1/2-inch rimmed baking sheet

• Tips: Check to be sure the brand of extract you select is labeled gluten-free. For certified gluten-free extracts, look for Nielsen-Massey brand at specialty-food markets and online at kingarthurflour.com.
• Agave syrup or nectar is the naturally sweet juice extracted from the agave plant. It has a lower glycemic index and is lower in calories than table sugar, but is even sweeter. Use it in moderation when substituting for table sugar. Look for it near other sweeteners in large supermarkets and natural foods stores.
• Pasteurized dried egg whites are a wise choice in recipes that call for uncooked egg whites. Look for brands like Just Whites in the baking or natural-foods section of most supermarkets. Reconstitute according to package directions or the recipe.
• To improvise a double boiler, bring 2 inches of water to a simmer in a large saucepan; set a medium or large metal bowl over the simmering water. Allow at least an inch between the water and the bottom of the bowl.

Nutrition