Preheat your oven to 350°F (175°C).
Grease and flour two 9-inch round cake pans.
In a large mixing bowl, cream the softened butter and granulated sugar until light and fluffy.
Add eggs one at a time, mixing well after each addition.
Stir in the orange zest and juice, mixing until fully combined.
In a separate bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
Gradually add the dry mixture to the wet ingredients, alternating with the buttermilk, starting and ending with the dry ingredients.
Fold in the chocolate chips if using.
Divide the batter evenly between the prepared pans and smooth the tops.
Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.
Let the cakes cool in the pans for 10 minutes before transferring to a wire rack to cool completely.
Once completely cool, frost with your choice of icing or enjoy plain.