Begin by preheating your oven to 350°F (180°C) with conventional heat only, leaving the fan off. Lightly grease a 30 × 22 cm, 12 × 9 inch baking pan so the cake releases easily after baking.

In a large mixing bowl, whisk the eggs and sugar together until the mixture becomes thick, pale, and airy. Taking the time to beat them well will help create a wonderfully soft sponge.

Pour in the vegetable oil and milk, then mix until everything is fully blended.

Add the flour, cocoa powder, baking powder, and vanilla. Stir gently just until the batter is smooth and no dry streaks remain. Avoid overmixing to keep the cake tender.

Spread the batter evenly into the prepared pan and bake for 15 to 16 minutes. The cake is ready when a toothpick inserted into the center comes out clean.

While the cake is in the oven, prepare the soaking syrup. In a saucepan, combine the milk, cocoa powder, vegetable oil, and sugar. Place over medium heat and stir continuously until the mixture reaches a gentle simmer.

Measure out 300 ml, 1½ cups, of the hot syrup into a separate bowl. Add the chopped dark chocolate and stir until it melts completely, creating a rich, glossy chocolate sauce.

Allow the baked cake to cool in the pan for about 10 to 15 minutes. Using a toothpick or skewer, poke small holes across the entire surface so the syrup can soak deep into every bite.

Gradually pour the warm cocoa syrup over the cake, giving it time to absorb before adding more. Once the syrup has soaked in, finish by drizzling the smooth chocolate sauce evenly over the top.

For the richest flavor and the most luscious texture, cover the cake and chill it overnight before serving. The extra resting time allows every layer to become perfectly moist and full of chocolate flavor.