Prep the pan: Line a baking sheet with parchment paper. Draw two rectangles about 25 x 8 cm (10 x 3 inches). Flip the paper so pencil marks don’t touch the batter.
Make the meringue: In a clean bowl, whip the egg whites with a pinch of salt until soft peaks form. Slowly add the sugar while whipping until glossy stiff peaks hold.
Prepare the sponge batter: In another bowl, beat egg yolks with sugar and vanilla until pale and thick. Gently fold in flour and cornstarch.
Pipe the layers: Transfer the meringue to a piping bag. Pipe three long strips in each rectangle outline. Fill the spaces between strips with sponge batter. You’ll have alternating sponge and meringue.
Bake: Bake at 150°C (300°F) for 25–30 minutes until the sponge is golden and the meringue firm but not browned. Cool completely.
Whip the cream: Beat the cream with powdered sugar until soft peaks form. Add espresso if using.
Assemble: Cut each baked rectangle in half lengthwise. Place one strip on a plate, spread whipped cream (and jam or berries if using), then add another strip on top. Repeat layering. Dust with powdered sugar.
Serve: Slice into portions and enjoy with coffee or tea.
