For the filling:
1. This buttercream is a little different.
2. In the mixer and with the flat attachment, soften the butter a little so that it takes on a smooth texture. Cocoa can be added here or it can be added at the end of the pastry cream, when it comes out of the pot.
When the pastry cream is relatively cold and settled, add to the butter and incorporate completely.
For assembly:
Unmold and remove the parchment paper from the cake.
On that same side, put the filling and distribute it evenly throughout the cake. If desired, you can add pieces of toasted walnuts for a finely flirtatious detail.
Roll completely, starting with the inward edge.
remove the ends for a better finish.
decorate with rosettes on top and chocolate decorations.
