Preheat the oven to 350 degrees. Line a jelly roll pan with parchment paper with the paper sticking up at the sides.
Whisk the flour, cocoa, baking powder and salt together in bowl and set aside.
Crack and separate the egg yolks and whites. Read my Diva’s Tip for a helpful hint during this process.
In a large bowl, whisk the egg yolks and sugar together on high until the mixture is pale yellow and leaves a stream when you lift up the whisk, about four minutes.
Add the sour cream, melted butter, and vanilla extract and whisk until well combined, about two to three minutes.
Slowly add the prepared dry ingredients and gently whisk together until well blended.
Whip the egg whites in a separate bowl until stiff peaks form.
Gently fold the whipped egg whites with the chocolate mixture until well combined.
Don’t worry if you still see some egg white foam in the mixture.
Spread the cake batter in the jelly pan and bake for 10 minutes. The cake should spring back when touched.
Remove the cake from the oven. Lift it from the pan using the extra parchment paper as handles and place it on a cold counter.
Using the parchment paper, start at the short end of the cake and slowly roll it up. Set the roll aside to cool completely.
This is where I make the chocolate bark. Simply use the same jelly pan relined with wax paper. Spread chocolate chips around the pan and place them in the cooling oven. Remove the chips after approximately two minutes and smooth the melted chocolate. Create long-stroke patterns to make the chocolate look like bark.
Refrigerate for an hour until the chocolate easily breaks apart.
After the cake has cooled, carefully unroll it using an offset spatula if necessary to prevent sticking. Don’t worry about the cake “cracking” in places. Keep unrolling until flat.
Add the heavy whipping cream, powdered sugar, vanilla extract, and salt to a large mixing bowl and whip at a high speed until stiff peaks form.
Spread the whipped cream filling evenly onto the unrolled cake then roll it back up with the parchment paper. Again, don’t worry about cracks in the cake. The cracks will be covered by frosting and chocolate bark.
Gently cut off a piece of the log at a slight angle. Place the original roll onto a decorative platter of your choice and attach the angled piece to the side. Refrigerate for an hour to firm up.
To make the ganache frosting, add the chopped chocolate bars into a medium-sized bowl. Heat the heavy whipping cream in the microwave until a slight boil. Immediately remove and pour over the chocolate. Let sit for a few minutes and whisk until smooth.
Let cool to room temperature.
Spread the ganache all over the log.
Adhere the broken bark pieces to cover the log completely.
Roll slightly moistened cranberries and rosemary sprigs in sugar and place them around the bûche de Noël.