Step 1: Make the Chocolate Sponge Cake

1. Preheat & Prep: Preheat oven to 375°F (190°C). Line a 10×15-inch jelly roll pan with parchment paper.
2. Mix Dry Ingredients: In a bowl, whisk together flour, cocoa powder, baking powder, and salt.
3. Beat Eggs & Sugar: In a large bowl, beat eggs and sugar on high speed for 3-4 minutes until pale and fluffy.
4. Add Vanilla & Milk: Gently mix in vanilla extract and milk.
5. Fold in Dry Ingredients: Sift the dry ingredients into the egg mixture and fold gently until just combined.
6. Bake: Spread the batter evenly in the prepared pan and bake for 10-12 minutes, or until the cake springs back when touched.

Step 2: Roll the Cake

7. Dust with Sugar: Lay a clean kitchen towel on the counter and dust it with powdered sugar.
8. Roll While Warm: Immediately invert the cake onto the towel, remove the parchment paper, and roll it up from the short end with the towel inside. Let cool completely.

Step 3: Make the Filling

9. Whip the Cream: Beat heavy cream, powdered sugar, and vanilla until stiff peaks form.

Step 4: Assemble the Yule Log

10. Unroll the Cake: Gently unroll the cooled cake and spread the whipped cream evenly over the surface.
11. Re-Roll: Roll the cake back up (without the towel) and place it seam-side down on a serving platter. Chill while making the ganache.

Step 5: Make the Chocolate Ganache

12. Heat Cream: In a saucepan, heat heavy cream until steaming (not boiling).
13. Melt Chocolate: Pour the hot cream over chocolate chips and butter, let sit for 1-2 minutes, then stir until smooth.
14. Cool & Frost: Let the ganache cool slightly, then spread it over the rolled cake, creating a log-like texture using a fork.

Step 6: Decorate & Serve

15. Dust with powdered sugar for a snowy effect, add chocolate shavings, berries, or meringue mushrooms for a festive touch.
16. Chill for 1 hour before slicing and serving.