Rolled cakes shaped like yule logs are a holiday classic in Europe. The cake is a modified angel food cake that gets extra tenderness from almond flour.
1. To make Cake: Preheat oven to 350°F. Line 17- by 12-inch rimmed baking sheet with parchment paper, and coat with cooking spray.
2. Lightly toast almonds on separate baking sheet 3 to 4 minutes. Set aside.
3. Beat egg whites 1 minute on low speed until frothy. With mixer still running, gradually add 1/4 cup sugar, and beat 1 minute. Gradually add remaining 1/4 cup sugar, increase speed to medium-high, and beat 5 minutes, or until egg whites are firm and glossy and soft peaks form. Beat in vanilla extract, almond extract, and salt.
4. Fold almond flour into egg whites with rubber spatula. Spread mixture on prepared baking sheet to 1/4-inch thickness using metal spatula. Sprinkle with 1/3 cup almonds. Bake 10 minutes, or until Cake is pale brown on top. Cool 5 minutes.
5. Run knife around sides of Cake, and turn out onto large, clean kitchen towel. Peel away parchment. Starting from short end, roll towel and Cake into log, incorporating towel as you go. Place log seam side down on wire rack to cool.
6. To make Ganache: Melt bittersweet and milk chocolates in double boiler until no lumps remain. Remove from heat, and stir in sour cream until smooth, then whisk in butter and salt. Cool until Ganache is thick and spreadable.
7. Gently unroll Cake on work surface. Spread Ganache over inside. Roll Cake into log, starting with short end, using towel to lift Cake, but without wrapping inside. Wrap towel around log, transfer to baking sheet, and chill 30 minutes. Remove towel. Frost outside of Cake log with remaining Ganache. Slice off each end of log to reveal roulade pattern inside, and “glue” ends to sides of log to mimic knots; frost with more Ganache. Lightly drag tines of fork down log to create bark pattern. Decorate with additional 1/3 cup almonds and confectioners’ sugar for snow, if desired.