01 -
Preheat the oven to 165°C. Line a 20 cm square baking pan with parchment paper, ensuring the paper extends slightly up the sides.
02 -
Place the egg yolks in a mixing bowl. Add water and sugar, then beat on high speed until pale and increased in volume.
03 -
Gradually drizzle in melted butter, add vanilla extract and salt, and continue beating until fully incorporated and the mixture is light.
04 -
Sift flour and cocoa powder together. Gradually add them to the yolk mixture, mixing thoroughly and scraping the sides and bottom of the bowl as needed.
05 -
Slowly add the warmed milk in portions, mixing gently until evenly combined. The resulting batter will be very thin.
06 -
In a separate clean bowl, add egg whites and vinegar. Whisk with a hand mixer until stiff peaks form.
07 -
Gently stir a small amount of whipped egg whites into the chocolate mixture to lighten it. Then, add portions of the chocolate batter into the remaining egg whites, continuing to stir gently. Repeat until combined, leaving visible white bits floating on top—avoid overmixing.
08 -
Pour the batter into the prepared pan. Bake for approximately 60 minutes, or until the edges are set, the centre is just set but jiggles slightly, and the top is golden brown.
09 -
Allow the cake to cool completely at room temperature. Cover and refrigerate for at least 4 hours to set fully before slicing into squares and serving.