Prepare the pan and oven

• Line a 28 x 28 cm cake pan with a baking mat.
• Preheat the oven to 170 °C.

Whisk the yolks with sugar

• Whisk the egg yolks with the sugar until pale and slightly thickened.

Add the dry and warm ingredients

• Sift in the plain flour and mix gently until just combined.
• Stir in the melted butter, salt and warm milk until the batter is smooth.

Whip the meringue

• Whip the egg whites with the lemon juice and vanilla extract.
• Gradually add the sugar and whip to soft, glossy peaks.

Fold and sift the batter

• Fold the meringue into the yolk batter in batches with a spatula.
• Sift the batter once more for an extra smooth texture.

Bake the sponge

• Pour the batter into the prepared pan and spread it evenly.
• Bake until the top springs back and is lightly golden.

Cool the sponge

• Turn the sponge out onto a cooling rack.
• Let it cool completely before filling.

Make the cream filling

• Whip the cold whipping cream with the sugar to firm peaks.

Fill and roll

• Spread the cream filling evenly over the cooled sponge.
• Roll the cake up tightly from the short side.
• Chill the roll before slicing.