- For the filling, prepare the German buttercream. Start by heating 500ml of milk in a pot over medium heat, and whisk in 120g of sugar and 40g of corn starch. Stir constantly to avoid lumps, and cook until the mixture thickens to a custard-like consistency. Once thickened, remove the mixture from the heat and let it cool for a few minutes.
- In a separate bowl, whisk 100g of egg yolk until smooth. Gradually add the warm custard mixture to the egg yolk, stirring constantly to prevent the egg yolk from curdling. Once fully combined, return the mixture to the stove and cook over low heat until it thickens further. Add vanilla extract to taste for extra flavor.
- Let the custard cool to room temperature, and once cooled, gradually add 660g of softened butter to the mixture. Beat the butter and custard together until fully incorporated, creating a smooth and fluffy buttercream. At this point, you can add 70g of cocoa powder to the buttercream for a rich chocolate flavor, or mix it in later for a swirled effect. The buttercream should be creamy and spreadable.
- Once the pionono is chilled and the buttercream is ready, it’s time to assemble the Swiss roll. Unroll the chilled cake and carefully remove the parchment paper. Spread a generous layer of the buttercream evenly over the entire surface of the cake, leaving a small border around the edges. For an extra touch, you can add pieces of toasted walnuts or any other chopped nuts for added texture and flavor.
- Once the filling is spread evenly, carefully roll the cake back up, starting from the edge that is closest to you. Roll tightly but gently, ensuring that the filling stays intact inside the cake. Once fully rolled, trim the ends of the cake for a neat finish. Decorate the top of the Swiss roll with rosettes of remaining buttercream and chocolate decorations for an elegant, professional look.
Storage and Serving
Chocolate Swiss Roll is best served fresh but can be stored in an airtight container in the refrigerator for up to 3 days. The cake will keep its flavor and texture for a short period, but the sooner it is enjoyed, the better. You can also freeze it for longer storage—just wrap the roll tightly in plastic wrap and aluminum foil and store it in the freezer for up to 1 month. To serve, let the roll thaw in the refrigerator overnight before enjoying.
Additional Tips
- For a lighter cake, you can reduce the amount of sugar in the sponge cake batter slightly.
- If you want a sweeter filling, feel free to add more sugar to the buttercream according to your taste.
- For a more festive look, top the roll with fresh berries or a dusting of cocoa powder before serving.
