1-Start with the raspberry filling by whisking 100 grams granulated sugar and 15 grams cornstarch together, then add 120 ml water and 15 ml fresh lemon juice. Heat the mixture until the sugar dissolves, stir in 170 grams fresh raspberries, and cook until it thickens before cooling it in the refrigerator.

2-For the chocolate cake, mix the dry ingredients: 95 grams all-purpose flour, 30 grams Dutch-processed cocoa powder, 2 grams baking powder, 2 grams espresso powder, and 1 gram salt. In another bowl, whisk the egg yolks with 150 grams granulated sugar, then add 120 grams sour cream, 60 grams melted butter, and 5 ml vanilla extract. Fold in the dry ingredients, whip the egg whites to stiff peaks, and gently fold them into the batter.

3-Pour the batter into a jelly roll pan and bake at 175°C (350°F) for 10-12 minutes. While the cake is hot, roll it with parchment paper and let it cool. Once cool, unroll it carefully. At this point, whip 240 ml cold heavy whipping cream with 30 grams powdered sugar, 15 grams natural unsweetened cocoa powder, and 5 ml vanilla extract until stiff peaks form for the chocolate whipped cream filling.

4-Spread the raspberry filling over the unrolled cake, then pipe the chocolate whipped cream on top. Re-roll the cake without the parchment paper, wrap it in plastic wrap, and refrigerate for at least one hour to firm up. For the ganache, heat 120 ml heavy whipping cream until boiling, pour it over 170 grams finely chopped semi-sweet chocolate, and stir until smooth. Chill the ganache until firm, reheat it slightly, and spread it over the chilled cake. Finally, decorate with optional whipped cream and fresh raspberries, and serve chilled or right away.