Flourless Walnut Yule Log with Chestnut Filling and Chocolate Buttercream

I've always wanted to make a yule log or what the French call a Bûche de Noël. A few years ago I took the risk and made a really successful one. Now I've made it a family tradition to bake a yule log or roulade almost every December. But actually roulades (fatörzs) have been a tradition in my family for quite some time. My great Aunt Piroska, who was actually my dad's aunt, used to make roulades every time we visited Hungary. I clearly remember eating a slice of her famous roulade on my 15th birthday. Unfortunately I haven't eat one like hers since. So I decided to make the tradition my own. This is my version of the traditional rolled cake. But instead of making the cake with flour, I use ground walnuts, resulting in a light and nutty sponge.

This cake is completely Hungarian in many ways. First, in Hungary rolled cakes and spongecakes (piskóta) are quite popular, and are often made for holidays and family gatherings. Second, walnuts are commonly used in many Hungarian cakes, like the famous Eszterházy, featuring walnuts in the sponge cake and filling. It's my absolute favorite! Thirdly, chestnuts are also typically used in recipes, the most popular of which is a chestnut purée dessert. Cooked chestnuts are puréed and flavored with sugar, rum, vanilla and cream. The mixture is then riced with a potato ricer over a plate and served with whipped cream. Trust me, it's delicious! With my yule log recipe I decided to combine these three traditional Hungarian desserts.

I think you will find this cake to be highly irresistible, especially when you take the extra step in decorating it with meringue mushrooms. They're fun to make and even more fun to pop in your mouth. Kids especially love them. Some things to look out for: Since the cake is flourless, it does shrink after baking, so don't be surprised. Also, make sure to roll the cake up soon after you've removed it from the oven. This way the cake takes on "muscle memory" and will be much easier to roll up after you've spread it with chestnut filling. Lastly, decorating is easy: All you have to do is run a fork through the buttercream to create ridges that look just like real bark. Happy holidays!

Flourless Walnut Sponge Cake

6 large eggs, separated
6 tablespoons confectioners sugar, sifted
1-1/4 cups ground walnuts
1 teaspoon baking powder
chestnut filling, recipe follows
dark chocolate buttercream, recipe follows
meringue mushrooms, recipe follows
dark chocolate bar

Preheat oven to 350 degrees F. Butter a rimmed baking sheet, line with parchment paper, and butter again.

In a small bowl, beat egg yolks by hand. In another small bowl, stir together dry ingredients: ground walnuts and baking powder.

In a stand mixer fitted with the whisk attachment, beat egg whites, adding sugar a little at a time, until soft peaks form. On low speed, drizzle in egg yolks. Fold in dry ingredients by hand until just combined.

Spread mixture evenly into prepared baking sheet. Bake for about 15 minutes or until edges are lightly golden. Immediately turn cake out of baking sheet onto a linen towel. Remove parchment paper and flip cake so that bottom is in contact with towel, and roll cake with towel. Set aside for at least 20 minutes, so that it takes on a rolled shape.

Unroll cake and spread evenly with chestnut filling. Roll cake starting from the edge, making sure to roll tight enough so that the cake makes contact with the filling, but not so tightly that all the filling comes out. Wrap in a towel and chill for at least 20 minutes.

Unwrap rolled cake and place seam-side down on an overturned baking sheet. Frost cake with chocolate buttercream, working from top down onto sides; frost the ends as well. Using a fork, create bark-like ridges. Chill for at least 20 minutes.

Using a hot knife, slice a portion of one end at an angle. Remove and attach to the top of cake. Use leftover frosting for spot coverage on slice. Using two offset metal spatulas, carefully transfer cake to a serving platter. Decorate cake with meringue mushrooms, adhering them with leftover buttercream. Shave a dark chocolate bar with a vegetable peeler, and decorate perimeter of platter with shavings. Dust the finished log with confectioners sugar. Yield: 10 to 12 slices.

Chestnut Filling

1 pound chestnuts
1/2 cup (1 stick) unsalted butter, room temperature
1 cup confectioners sugar, sifted
3 tablespoons rum
3 tablespoons heavy cream
1/2 teaspoon pure vanilla extract

Using the point of a sharp paring knife, carefully peel outer shells of chestnuts, leaving inner shells intact.

Add peeled chestnuts to a pot of water with 1 tablespoon granulated sugar. Make sure chestnuts are covered with 1 to 2 inches of water. Bring to a boil and let simmer for about an hour or until chestnuts are knife tender.

Remove and discard inner shells of chestnuts. While still warm, press chestnuts through a sieve or potato ricer. Discard particles remaining in sieve.

In a standing mixer fitted with the paddle attachment, cream butter until light and fluffy. Beat in sugar on medium-low speed a little at a time until combined. Add chestnut purée and mix until combined. Add rum, heavy cream, and vanilla; mix until incorporated. Yield: just enough filling for cake.

Dark Chocolate Buttercream

1 cup confectioners sugar
2 tablespoons cocoa powder
4 ounces (1/2 cup) dark chocolate, finely chopped or chips
1 cup (2 sticks) unsalted butter, room temperature

Sift together the dry ingredients: sugar and cocoa powder.

On medium-low heat, melt chocolate in a heat-proof bowl set over a pot of simmering water.

In a standing mixer fitted with the paddle attachment, cream butter until light and fluffy. Beat in dry ingredients on medium-low speed a little at a time until combined. Add the melted chocolate and beat until incorporated. Yield: enough frosting for one log, plus a little extra for the meringue mushrooms.

Meringue Mushrooms

4 large egg whites
1-1/4 cup granulated sugar
1 teaspoon lemon juice
2 tablespoons cocoa powder

Preheat oven to 250 degrees F. Line a baking sheet with parchment paper or a Silpat.

In the bowl of a stand mixer fitted with the whisk attachment, start beating the egg whites until frothy. Pour in sugar and lemon juice, and continue beating until the mixture is glossy and stiff peaks form.

Transfer meringue to a pastry bag fitted with a 1/2-inch plain round tip. To create mushroom caps, pipe rounds larger than a quarter onto the baking sheet by applying uniform pressure. If there's a little peak, tap it down with a moistened finger. To create stems, pipe rounds smaller than a penny and pull the piping tip upward about an inch. Make sure to pipe as many stems as there are caps for an even number.

Dust the mushrooms caps with cocoa powder. Bake for about an hour or until the meringues are firm to the touch. Cool completely before assembly.

To assemble the mushrooms, start by creating a small hole in the underside of each cap using a knife. Pipe or spread a small amount of leftover buttercream in the hole, and insert a stem. Repeat process until all mushrooms are constructed. Yield: 18-20 meringue mushrooms.

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