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

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

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

Gradually pour the wet ingredients into the dry ingredients, mixing gently until just combined.

Pour the batter into the prepared jelly roll pan, spreading it evenly.

Bake for 12–15 minutes. Check with a toothpick to ensure it's properly set.

While baking, dampen a kitchen towel and dust it with powdered sugar.

Once baked, cool the cake in the pan for 5 minutes, then invert onto the powdered sugar towel.

Roll the cake up with the towel, starting from one short end, and let it cool completely.

In a medium bowl, beat heavy whipping cream until soft peaks form, then mix in powdered sugar and vanilla extract until stiff peaks.

Unroll the cake, spread a layer of frosting, and roll it back up without the towel.

Dust the top of the rolled cake with a mixture of cocoa powder and powdered sugar, and add chocolate shavings or sprinkles.

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