Preheat your oven to 350°F (175°C) .Line an 8x8 pan with parchment paper.
In a large mixing bowl, sift together the all-purpose flour, unsweetened cocoa powder, baking powder, baking soda, salt, and granulated sugar. Mix well until combined.
Add egg, vanilla, oil and milk and warm water. Stir gently until just combined. Avoid overmixing.
Pour the batter into the prepared pan and bake for 35-40 minutes or until a toothpick inserted into the center of the cakes comes out clean.
Once baked, remove the cake from the oven and allow it to cool in the pan for about 10 minutes.