In a mixing bowl, beat the eggs and sugar until light and creamy.
Add the vanilla extract and melted butter, then mix to combine.
Sift the plain flour and cocoa powder into the bowl. Then add the baking powder and salt. Mix until fully incorporated.
Grease a baking dish with butter and pour in the batter, spreading it evenly.
Cover the dish with aluminium foil and bake in a preheated oven at 160°C (fan-forced) / 320°F for 35-40 minutes, or until a skewer inserted comes out clean.
Once baked, use a skewer or souvlaki stick to poke holes all over the cake.
While the cake is still hot, slowly pour the cooled syrup over the sponge, allowing it to absorb evenly.
Let the cake cool completely before moving on to the next layer.