Preheat Oven & Prep Tray: Set oven to 180ºC (356ºF). Grease and line a 8-inch x 12-inch (20cm x 30cm) cake pan, leave overhang to easily remove cake. Set aside.
Mix Dry Ingredients: Sift together the flour, cornflour, and baking powder in a medium size bowl. Set aside.
Prepare Butter: Melt the butter and set it aside to cool slightly, without letting it solifify.
Beat Eggs: In a stand mixer or with an electric hand beater, beat room temperature eggs for 1 minute and 30 seconds until light and frothy.
Add Sugar: Gradually add the sugar, 1/3 at a time, beating for 15 seconds after each addition. Scrape down the sides.
Test Consistency: Lift the whisk and drizzle the batter in a figure 8 shape. The batter should form thick ribbons and briefly hold its shape atop the mixture. See the provided image in the blog post for reference.
Add Butter and Milk: Gently fold in melted butter and milk without over-mixing, ensuring to keep as much air as possible in the batter.
Fold in Flour: Sift in half of the flour mixture and gently fold into the eggs, then repeat with the remaining flour. Fold until no streaks of flour remain, avoiding over-mixing.
Transfer Batter: Pour the batter into the lined pan, smooth the top out evenly.
Bake: Bake for 18-20 minutes. Let it cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.