In a small saucepan, combine the freshly squeezed lemon juice, lemon zest, caster sugar, and egg yolks. Warm over low-medium heat, stirring constantly until thickened, about 10 minutes.

Melt the white chocolate using a double boiler or microwave until smooth, being careful not to overheat.

Gradually pour the lemon mixture over the melted chocolate in three additions, mixing until fully incorporated. Transfer to a bowl, cover tightly with cling film, and refrigerate overnight to set.

Preheat your oven to 340°F (170°C) and line a baking sheet with parchment paper.

Beat egg whites until soft peaks form. Gradually add sugar, then egg yolks, and fold in sifted flour and cornstarch until well combined.

Pour batter into the prepared baking sheet, spread evenly, and bake for 8-10 minutes until springy and lightly golden.

Cover the sponge with a damp towel, invert onto the towel to cool. Brush the surface with lemon-sugar syrup before spreading chilled lemon curd evenly over the sponge.

Starting from the shorter side, carefully roll the sponge cake with the filling inside, wrap tightly in a towel, and refrigerate for about an hour.

Combine water and sugar in a saucepan, heat until it reaches 240°F without stirring. Start whipping egg whites in a stand mixer until foamy, and gradually stream in hot sugar syrup until stiff peaks form.

Unwrap the roulade, position it on a serving platter, trim ends if necessary. Spread Italian meringue generously over the roulade.

Lightly toast the meringue with a handheld torch to achieve a golden color and subtle caramelization.