Separate 4 large eggs into yolks and whites in two bowls. Warm 60g vegetable oil in the microwave for 40 seconds and set aside.

Sift 40g all-purpose flour and 20g unsweetened cocoa powder into the bowl of oil. This ensures a smooth, lump-free batter.

Add 60g sugar-free milk (room temperature) and 4 egg yolks to the dry mixture. Whisk until smooth and velvety.

Gradually add 70g granulated sugar to the egg whites and beat until soft peaks form. The whites should hold their shape without collapsing.

Add a small scoop of egg whites to the cocoa mixture to lighten it. Gently fold the rest of the egg whites into the batter without deflating it.

Line a 15 x 15 x 7 cm square mold with parchment paper and wrap it in foil. Place the mold in a water bath with 80°C hot water filling halfway up the sides.

Pour the batter into the mold and bake at 150°C for 50 minutes. The water bath ensures an even bake and prevents cracking.

Remove the cake from the mold and peel off the parchment paper. Let it cool completely on a wire rack before slicing and enjoying.