Preheat your oven to 350°F (175°C) and line a 10×15-inch jelly roll pan with parchment paper, leaving an overhang for easy removal.

In a large bowl, whisk 4 eggs and 1/2 cup granulated sugar on high speed for 5 minutes, or until the mixture is pale, thick, and ribbons form when you lift the whisk.

Gently stir in 1 teaspoon of pure vanilla extract until just combined, being careful not to deflate the batter.

Sift together 3/4 cup flour, 1 teaspoon baking powder, and a pinch of salt, then fold into the egg mixture in three additions, using a spatula to keep the batter airy.

Spread the batter evenly in your prepared pan and bake for 10–12 minutes, or until the top is lightly golden and springs back when touched.

While still warm, invert the cake onto a clean kitchen towel dusted with powdered sugar and peel off the parchment; roll the cake and towel together from the short end and let it cool on a wire rack.

In a chilled bowl, whip 1 cup heavy cream, 2 tablespoons powdered sugar, and 1/2 teaspoon vanilla extract to stiff peaks, using an electric mixer for best results.

Carefully unroll the cooled cake, spread a thin layer of raspberry jam if using, then dollop and evenly spread the whipped cream over the surface.

Gently re-roll the cake without the towel, wrap in plastic, and refrigerate for at least 20 minutes to set the shape.

Unwrap, dust with powdered sugar, top with fresh berries and sprigs of rosemary, slice, and serve chilled or at room temperature.