Preheat oven to 375°F. Line an 11x17" sheet pan with parchment paper leaving an overhang on the short edges and grease the paper.

Beat egg whites in a stand mixer with whisk attachment on medium speed until foamy.

With the mixer running, gradually add 1/2 cup of the sugar, about a tablespoonful at a time, beating to incorporate before adding more.

Increase speed to high and beat until medium-stiff peaks form.

Scrape egg whites into a separate bowl and return bowl to the stand mixer.

Add egg yolks to same stand mixer bowl with remaining 1/3 cup sugar and beat with whisk attachment on medium speed until creamy and lightened in color, about 2 minutes.

Reduce speed to low and beat in vanilla.

In a separate bowl, whisk together the flour, cocoa, baking powder and salt.

Add 1/3 of the flour mixture to stand mixer with yolks and beat on low speed to incorporate.

Add 1/2 of the milk and beat on low again.

Repeat with remaining flour mixture and milk (for a total of 3 additions of flour mixture and 2 additions of milk). Only beat until just combined.

Remove mixer bowl from stand mixer. Fold in egg whites with a large silicone spatula.

Scrape batter onto prepared pan and spread evenly into the corners.

Bake 10 to 12 minutes, or until it loses its shine and the center feels slightly springy.

Let cool a few minutes in the pan until you can handle the cake without burning your fingers. Roll the cake up in the parchment paper, starting with the short edge, and transfer the roll to a cooling rack to cool completely.

When cake is completely cold, gently unroll it on a work surface. Leave it on top of the parchment.

Spread the chocolate cream filling evenly over the cake. Roll it back up (gently peeling it off the parchment this time) and place it seam-side down on a serving dish.

Trim away the less-than-pretty end slices and discard if desired.

In a microwave-safe bowl, combine the heavy cream and chopped chocolate.

Microwave in 20-second bursts, stirring well between each, until the chocolate is completely melted and the mixture is smooth.

Let it cool slightly to thicken before spreading on your Buche de Noel. Use a fork to create bark-like lines.

Cover with plastic wrap and refrigerate if not serving right away. It's easier to slice if you chill it for 2 hours. Decorate with sugared cranberries and rosemary just before serving.