Preheat the oven to 350°F (175°C) and grease two round cake pans.

In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, and salt until well combined.

In another bowl, whisk eggs, milk, oil, orange juice, orange zest, and vanilla until smooth.

Gradually add the wet ingredients to the dry mixture and stir gently until just combined.

Pour batter evenly into prepared pans and bake for 30-35 minutes or until a toothpick comes out clean.

Allow cakes to cool in pans for 10 minutes before transferring them to wire racks to cool completely.