Preheat your oven to 180 degrees Celsius (160 degrees if using a fan oven). Line a high-sided tray (25 x 35 cm) with baking paper.
Prepare the Dough:
In a bowl, mix together the wheat flour, cornstarch, baking powder, and pinch of salt. Set aside.
Beat the Eggs:
In a metal bowl over a lukewarm water bath, beat the eggs, sugar, and vanilla sugar with a hand mixer until the sugar dissolves. Continue whipping for about 10 minutes until you have stable egg foam.
Combine Mixtures:
Sift the flour mixture over the egg foam and gently fold it in. Melt the butter and fold it with the milk into the mixture. Pour the batter into the prepared pan and bake for about 25 minutes.
Make the Soaking Liquid:
In a pot, combine sweetened condensed milk, evaporated milk, regular milk, and rum. Bring to a brief boil.
Assemble the Cake:
Let the sponge cake cool slightly, but while it’s warm, poke holes all over the surface using a fork or wooden stick. Pour the soaking liquid generously over the cake and let it cool completely.
Prepare the Topping:
Whip the cream with sugar, cream stiffener, and cinnamon until stiff peaks form. Spread it over the cooled cake and top with fresh strawberries.