• Make the filling and frosting before the cake. 

To make the filling:

• Make the mousse according to package directions in a large bowl. In a separate bowl whip the cream and whip it stabilizer until soft peaks form. Add in the powdered sugar and vanilla and whip until very stiff peaks form. Fold this into the mousse until all white streaks are gone and chill completely. This can be made a day ahead of time.

To make the frosting:

• Cream the butter until light and fluffy, about 2-3 minutes. Add in the cooled melted chocolate and mix again. Dissolve the espresso powder into coffee and add that into the mixture along with the salt and vanilla extract. Add in the powdered sugar one half cup at a time stopping the mixer when adding and scraping down the sides in-between additions. Once all the powdered sugar is added mix on slow to get rid of air bubbles as best  you can. Transfer to an air tight container until ready to use. If not using within 24 hours keep refrigerated. Thaw completely at room temperature and mix on low before using.

To make the cake:

• Preheat oven to 375 Deg. Grease an 11x17 jelly roll pan with butter, line with parchment and grease the parchment well. 
• In a stand mixer combine the egg yolks and ½ cup of the sugar and mix on high for 6 minutes, until the mixture is thick and very pale. Add in the cocoa powder on low along with the salt and vanilla. Keep mixing on low while you whip the egg whites. In a clean stainless or glass bowl whip the egg whites with the cream of tartar adding in the remaining ¼ cup of sugar halfway through mixing. Whip until stiff peaks are formed. Quickly fold the egg whites into the egg yolk mixture with a spatula then spread evenly over the prepared pan. 
• Bake for 10-12 minutes or until the center bounces back when pressed. Let cool for 5 minutes in the pan. While the cake is cooling generously dust a clean dish towel with powdered sugar. Remove the cake from the pan and flip it over onto the prepared dish towel. Carefully remove the parchment paper and gently roll up the cake in a pretty tight roll.
•  Let cool completely rolled up. 
• Gently unroll once cooled and spread the filling in the middle leaving just a little bit of space on the edges.
•  Place seam side down on a platter and chill until the filling firms up a little. 
• When ready to assemble cut one 2-3 inch end off the cake roll at an angle and the other at an even cut. Frost the big part of the cake, leaving the front cut piece exposed to see the “rings” of the log. Use a small spatula and “glue” the cut pieces with frosting to the bigger cake roll. Continue to frost the rest of the cake. Use frosting to glue the chocorooms cookies and sprinkle the chocolate curls on top a dust with powdered sugar “snow”.  Keep chilled covered in plastic wrap until ready to serve. Thaw and serve at cool room temperature.