Preheat oven to 350 degrees. Gather your equipment and ingredients so that you have everything close at hand at the counter or table. Line a jelly roll pan with parchment paper and grease with cooking spray.
Make the Sponge Cake
In a small bowl, combine all-purpose flour, cocoa powder, baking powder and salt.
In a large mixing bowl, beat egg yolks until thick. Add 1/2 cup granulated sugar and beat until pale. Mix in flour ingredients.
In another large bowl, whisk egg whites until foamy. Add remaining 1/4 cup sugar, a little at a time, along with vanilla and cream of tartar. Whisk until stiff peaks form.
Gently stir half of egg whites into cake batter, then fold in remaining egg whites to make a fluffy light batter.
Pour batter into prepared baking sheet and spread to edges in an even layer. Bake in preheated oven until cake springs back when lightly pressed, about 10-12 minutes.
Roll the Cake
Dust a clean kitchen towel with powdered sugar.
Run a thin knife around the cake edges. Invert warm cake onto towel. Carefully, remove the parchment paper from the cake.
Starting at the short end, use the towel to tightly roll cake into a log. Let cool completely rolled up.
Prepare the Filling and the Ganache Icing
To make the filling, in a large bowl, mix together the heavy cream, powdered sugar, vanilla extract, and salt. Whisk on high until stiff peaks form. Refrigerate until ready to use.
To make the Ganache Icing, place chocolate chips in a medium glass bowl. Add heavy cream. Microwave for 45-60 second intervals until the chocolate has melted, being careful not to overheat the chocolate. Let it sit for 7-10 minutes until the chocolate has melted, then stir to combine. Allow to cool until it has reached the right consistency for spreading.
Assemble the Yule Log
When the cake is cool, carefully unroll and spread filling evenly to the edges of the cake.
Roll back into a log, this time without the towel, and place seam side down on a platter. Refrigerate for 45 minutes.
Spread the cooled ganache onto the cake, spreading all over along the sides and also the front and back. Using a fork, mark the sides of the cake to give a ridged appearance of bark.
Store cake in refrigerator until time to serve. Before serving, dust lightly with powdered sugar. Serves 8-10.