Make the Chocolate Sponge Cake:

1. Preheat oven to 400°F. Spray a half sheet baking pan (17x12-inches) with nonstick spray and line it with parchment paper. Spray the parchment paper with nonstick spray.
2. In a medium bowl, whisk together flour, cornstarch, cocoa powder, and salt. Set aside.
3. Use a stand mixer or hand mixer to combine egg yolks, all but 2 tablespoons of sugar (set aside to be used with the egg whites), and vanilla in a large bowl. Beat together mixer on high speed until thick, fluffy and very pale yellow, about 4-5 minutes.
4. Sift in half the dry ingredients into the bowl, and fold it in with a silicone spatula until just incorporated. Repeat with the remaining half of dry ingredients.
5. In a medium bowl, beat egg whites on medium speed until soft peaks form, about 1-2 minutes. Gradually add in the remaining 2 tablespoons of sugar and beat on high speed until stiff peaks form, about 3-4 minutes.
6. Fold the egg whites into the batter using a silicone spatula, until just incorporated. Avoid overmixing and deflating the egg whites.
7. Carefully pour the batter into the prepared half sheet baking pan and gently spread it out using a small icing spatula. Bake for 8-10 minutes. The cake is done when it springs back when lightly poked with your finger and a toothpick comes out clean. The cake is quite thin so keep a close eye on it. Take it out as soon as it is done. If you overbake it, it will be dry and crack as it rolls.
8. Once the cake is done, it will look a little puffed up and bubbly on the top. It will shrink down within a minute. Let it sit for a minute or two, then immediately run a small icing spatula or knife around the edges of the pan to loosen the cake. Sift some confectioners' sugar on top to cover the cake. Flip the cake over onto a clean kitchen towel placed on the counter. Remove the parchment paper which was originally lining the baking pan. Sift the newly exposed side of the cake with confectioners' sugar. This will help prevent the cake from sticking to the towel when rolled.
9. Slowly and gently roll the cake from the narrow end with the towel until the entire cake is rolled and completely covered in the towel. The cake will be warm when first rolled. Allow the rolled up cake to cool completely in the towel, about one hour.

Make the Whipped Cream:

1. Use a stand mixer or hand mixer to whip the heavy cream with confectionary sugar and vanilla on medium speed until medium peaks form, about 2-3 minutes. Store in the refrigerator until ready to use.

Fill the Yule Log Cake with Whipped Cream:

1. When the cake has cooled down completely, gently and very slowly unroll the cake.
2. Using a small icing spatula, carefully spread the whipped cream evenly on top of the cake, leaving a 1-inch border uncovered around the cake.
3. Carefully and slowly roll the cake back up without the dish towel. Cover tightly with plastic cling wrap and refrigerate for at least 1 hour, up to overnight, to firm up before adding the whipped ganache topping.

Make the Whipped Chocolate Ganache Topping:

1. Place chopped chocolate into a medium bowl.
2. Heat the heavy cream in a small saucepan until it begins to simmer. Immediately remove from heat before it begins to boil.
3. Pour hot cream over top of the chopped chocolate, and let it sit for 5 minutes to allow it to soften the chocolate. Then use a spoon to slowly stir until completely combined. Allow the ganache to cool down and thicken uncovered in the refrigerator for 20 minutes.
4. Once the ganache has cooled down and is firm (but still soft), use a hand mixer to whip it on medium-high speed until fluffy, about 3-4 minutes.

Decorate the Cake with Whipped Chocolate Ganache:

1. Remove the cake from the refrigerator and carefully remove the plastic cling wrap.
2. Leave the yule log cake in tact and cut 1/2-inch from each side to make the edges even. You can also cut 4-inches off of one end of the yule log cake on angle and place it on the side of the roll to look like a tree branch.
3. Cover the cake with the whipped ganache and spread evenly using a small icing spatula. Draw lines using a fork to give it a wooden texture look like tree bark.