Line a 25 x 30 cm jelly roll pan with parchment paper, then whisk together the cake flour, softened butter, icing sugar, and egg white until smooth to make the pattern batter.
Tint a spoonful of batter pink, divide the rest in half, color one part black, and leave the other plain, then transfer each into piping bags and pipe ghost shapes onto the parchment, using a template if you prefer.
Place the baking sheet with the ghost design in the freezer for 1 hour to set while you start on the cake batter.
Preheat the oven to 160°C (320°F). Heat the milk in a small saucepan until steaming, then whisk it slowly into the egg yolks, vegetable oil, and sugar (I).
Sift in the cocoa powder and flour, whisk until smooth, then set aside. In another bowl beat the egg whites until foamy, gradually add sugar (II), and whip until stiff peaks form.
Fold the meringue into the yolk mixture in three additions until just combined, then pour the batter into the prepared pan over the frozen ghost design.
Bake for 25 minutes, remove from the oven, and invert the cake onto a clean sheet of parchment paper. Peel off the design paper, place a kitchen towel on top, flip again, and roll the cake up with the towel inside. Let it cool completely.
While the cake cools, whip the cream and sugar to soft peaks, add the vanilla bean paste, and beat until stiff peaks form.
Gently unroll the cooled cake, remove the towel, spread the whipped cream evenly inside, then re-roll tightly, wrap in plastic wrap, and chill for at least 2 hours before slicing and serving.