Make the Chocolate Sponge Cake:
Preheat oven to 350°F (175°C). Line a 10×15-inch jelly roll pan with parchment paper.
In a large bowl, whisk eggs and sugar on high speed for 5 minutes until pale and fluffy.
Add vanilla extract and milk, whisking to combine.
Sift together flour, cocoa powder, baking powder, and salt, then gently fold into the egg mixture until just combined.
Spread the batter evenly in the pan and bake for 10-12 minutes, until the cake springs back when touched.
While warm, carefully roll the cake in a clean kitchen towel dusted with powdered sugar. Let it cool completely.

Make the Chocolate Cream Filling:
In a mixing bowl, beat heavy cream, powdered sugar, cocoa powder, and vanilla extract until soft peaks form.
Carefully unroll the cooled sponge cake and spread an even layer of chocolate cream over the surface.
Gently roll the cake back up without the towel and place seam-side down on a serving tray.

Make the Chocolate Ganache Topping:
Heat heavy cream until hot but not boiling. Pour over the chopped chocolate and let sit for 1-2 minutes.
Stir until smooth, then mix in the butter for shine.
Let cool slightly, then spread or drizzle over the cake roll.

Decorate & Serve:
Arrange mini chocolate eggs on top and sprinkle with chocolate shavings or sprinkles.
Dust with powdered sugar for a festive touch.
Chill for 30 minutes before slicing and serving!