Prepare the Cake:
Preheat oven to 180 °C (350 °F). Line and grease a 10×15-inch jelly roll pan.
Whisk flour, cocoa, baking powder, and salt.
Beat eggs and sugar until pale and fluffy, then mix in vanilla and milk.
Gently fold in dry ingredients until combined.
Spread batter in pan; bake 12–15 minutes until cake springs back.

Roll the Cake:
Turn warm cake onto a towel dusted with powdered sugar.
Peel off parchment and roll cake with the towel. Cool completely.

Make the Filling:
Whip heavy cream, powdered sugar, and vanilla until stiff peaks form.

Assemble:
Unroll cooled cake, spread whipped cream, then re-roll tightly.
Place seam-side down on a platter.

Optional Ganache Topping:
Heat cream and pour over chocolate. Let sit, then stir smooth.
Cool slightly and pour over cake. Chill briefly to set.

• Prepare the Cake:
  Preheat oven to 180 °C (350 °F). Line and grease a 10×15-inch jelly roll pan.
  Whisk flour, cocoa, baking powder, and salt.
  Beat eggs and sugar until pale and fluffy, then mix in vanilla and milk.
  Gently fold in dry ingredients until combined.
  Spread batter in pan; bake 12–15 minutes until cake springs back.

• Roll the Cake:
  Turn warm cake onto a towel dusted with powdered sugar.
  Peel off parchment and roll cake with the towel. Cool completely.

• Make the Filling:
  Whip heavy cream, powdered sugar, and vanilla until stiff peaks form.

• Assemble:
  Unroll cooled cake, spread whipped cream, then re-roll tightly.
  Place seam-side down on a platter.

• Optional Ganache Topping:
  Heat cream and pour over chocolate. Let sit, then stir smooth.
  Cool slightly and pour over cake. Chill briefly to set.