Step 1: Preheat oven to 375°F (190°C). Line a 10x15 inch jelly roll pan with parchment paper, extending over the sides. Grease the parchment.
Step 2: In a large bowl, whisk egg yolks with 1/2 cup granulated sugar until light and fluffy. Stir in 1 teaspoon vanilla extract.
Step 3: In a separate bowl, sift together flour, cocoa powder, baking powder, and salt. Gradually fold the dry ingredients into the egg yolk mixture until just combined.
Step 4: In another clean bowl, beat egg whites until soft peaks form. Gradually add 1/4 cup granulated sugar and continue beating until stiff, glossy peaks form.
Step 5: Gently fold one-third of the egg whites into the chocolate batter to lighten it, then fold in the remaining egg whites until no streaks remain. Be careful not to deflate the mixture.
Step 6: Pour the batter evenly into the prepared jelly roll pan and spread to the edges. Bake for 10-12 minutes, or until the cake springs back when lightly touched.
Step 7: While the cake bakes, lay a clean kitchen towel on a flat surface and dust generously with powdered sugar or cocoa powder.
Step 8: Immediately after removing the cake from the oven, invert it onto the prepared towel. Carefully peel off the parchment paper.
Step 9: Starting from a short end, carefully roll the warm cake and towel together into a tight spiral. Place seam-side down on a wire rack and let cool completely (about 1-2 hours).
Step 10: While the cake cools, prepare the raspberry filling. Combine raspberries, sugar, and lemon juice in a small saucepan over medium heat. Bring to a simmer, crushing some berries.
Step 11: Stir in the cornstarch slurry and cook, stirring constantly, until the mixture thickens. Remove from heat and let cool completely.
Step 12: For the frosting, beat softened cream cheese and butter until smooth and creamy. Gradually add sifted powdered sugar, one cup at a time, beating until smooth. Stir in 1 teaspoon vanilla extract. If needed, add milk/cream for desired consistency.
Step 13: Once the cake is completely cool, gently unroll it. Spread an even layer of the cooled raspberry filling over the cake, leaving a small border around the edges.
Step 14: Carefully spread about half of the cream cheese frosting over the raspberry filling.
Step 15: Tightly re-roll the cake, without the towel this time. Place seam-side down on a serving platter.
Step 16: Frost the entire exterior of the Swiss roll with the remaining cream cheese frosting. Decorate with fresh raspberries or a dusting of cocoa powder, if desired.
Step 17: Chill the Swiss roll for at least 30 minutes before slicing and serving. This helps the frosting and cake set for cleaner cuts.