Preheat oven to 325 °F (163 °C). Line or lightly grease a 20 cm (8×8 inch) square baking dish.

Separate the eggs. In a clean bowl, whisk the egg whites until stiff peaks form. Set aside.

In another bowl, beat the egg yolks with sugar until pale and creamy. Add melted butter and vanilla extract, then mix until well combined.

Stir in the sifted flour until smooth and lump‑free.

Gradually pour in the lukewarm milk, mixing until the batter is very thin and homogenous.

Gently fold in the beaten egg whites by thirds, preserving airiness.

Pour into the prepared dish and bake for 40–60 minutes, starting to check around 40 minutes; top should be golden and firm, center slightly wobbly.

Cool completely before refrigerating for at least 2 hours or up to overnight—this helps the custard set into distinct layers.

Just before serving, dust with powdered sugar. Optionally serve with fresh berries or a berry coulis.