For the Fillings whipped cream
Preheat oven to 180C. Line a 28 x 28 cm flat square cake pan with parchment paper.
Combine egg, egg yolks and vanilla extract in a small bowl and beat lightly. Set aside.
Place butter in a small saucepan and heat gently until melted. Add flour to melted butter and cook through.
Transfer butter-flour mixture to a bowl, then add egg mixture a little at a time. With a spatula, mix into a smooth batter.
Add milk and mix to incorporate.
Strain batter and set aside.
To make meringue, place egg whites in a clean bowl and beat until foamy. Add half the sugar and continue beating for a few minutes, then add remaining sugar and beat until egg whites are glossy and stiff peaks form. The meringue is essential for the cake to rise, so it must be stiff and stable.
Add one-third of meringue to batter and fold in lightly, then add remaining meringue and fold through until just incorporated.
Pour batter into prepared cake pan and spread evenly with a scraper.
Place cake pan on a tray and bake for 20 minutes. Baking on an additional tray prevents the bottom of the sponge from browning too quickly.
When cake is done, remove from pan and wrap with cling wrap to cool. Cooling this way helps to retain its moisture.
Unwrap the cake, spread whipped cream evenly and arrange strawberries on the bottom end of the cake.
Gently roll up the cake.
Wrap the cake in parchment paper and twist both ends. Leave in the fridge for 30 minutes to set.
Use a serrated knife, trim both ends of the roll then slice into pieces. Serve.