Preheat your oven to 350°F (175°C) and line a 15x10 inch jelly roll pan with parchment paper.

In a large mixing bowl, sift together all-purpose flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt.

In a separate bowl, combine eggs, vegetable oil, vanilla extract, and buttermilk, then beat until smooth.

Fold the wet ingredients into the dry mixture until no visible flour streaks remain.

Pour the batter into the prepared pan and bake for 12-15 minutes or until a toothpick comes out clean.

Lay a damp kitchen towel sprinkled with powdered sugar while the cake bakes.

After baking, cool the cake for 5 minutes, invert it onto the towel, and roll it tightly to cool.

Whip the heavy cream until soft peaks form, then add powdered sugar and vanilla extract until stiff peaks form.

After cooling, unroll the cake and spread whipped cream frosting over it, then re-roll carefully.

Dust the rolled cake with cocoa powder and decorate with chocolate shavings or sprinkles.

Chill the decorated Yule Log in the refrigerator for at least one hour before serving.