• Melt the butter over a low heat. Once at the boil, leave for 5-10 minutes until it turns golden brown, with the brown residue visible on the bottom of the pan. Turn off the heat and strain the butter through a thin sieve. Leave to cool.
• Mix the egg yolks with the sugar. They should triple in volume, at least. Add the flour and the melted butter and mix gently.
• Heat up the milk and vanilla extract and gradually add it to the mixture, mixing continuously. The consistency will be fairly thin.
• Whisk the egg whites with a pinch of salt until they become stiff. Add to the mixture with a spatula mixing gently. Do not overmix, even if the mixture is not fully smooth.
• Preheat the oven to 160 °C (320 °F). Butter a 24/24cm (9.5/9.5 inch) non-stick baking tray. Pour the mixture into the tray. Bake for 45-50 minutes, until a nice golden brown.
• Leave the cake to cool in the tray for 1-2 hours and then slice it into delicious cubes. Sprinkle with powdered sugar and serve.

Enjoy!