Preheat your oven to 350°F.
Butter and flour a 10-inch Bundt pan to prevent sticking.
In a large mixing bowl, beat the softened butter and sugar until fluffy and pale, about 5 minutes.
Mix in the eggs one at a time, ensuring each egg is well incorporated before adding the next.
Add the orange zest and mix well.
In another bowl, sift together the flour, baking powder, baking soda, cocoa powder, and salt.
Slowly add the dry ingredients to the wet mixture, alternating with the buttermilk and orange juice.
Mix until just combined.
Add vanilla extract and stir briefly.
Pour the batter into the prepared Bundt pan.
Tap the pan gently on the counter to remove any air bubbles.
Bake for 45-55 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes.
Carefully invert the cake onto a wire rack to cool completely before serving.