Preheat the oven to 350°F (175°C). Grease and line an 8x8-inch (20x20 cm) square baking pan with parchment paper.
In a mixing bowl, beat the eggs and sugar together until the mixture becomes pale and fluffy. This step is crucial for incorporating air into the batter, giving the cake its signature light texture.
Gradually add the oil and milk while continuing to mix.
In a separate bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt.
Gently fold the dry ingredients into the egg mixture until well combined. Be careful not to overmix, as this can lead to a dense cake.
Stir in the vanilla extract and brewed coffee or rum for extra richness.
Pour the batter into the prepared pan and bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool completely before slicing it in half horizontally.