In a mixing bowl sift together cake flour and baking powder, set aside
In a separate bowl whisk together buttermilk, vanilla extract, and the juice from the remaining 3 oranges
In a stand mixer bowl cream softened butter and granulated sugar until light and fluffy; approximately 5 to 7 minutes
Add eggs one at a time, mixing just until incorporated after each addition
Alternate adding dry and wet mixture to creamed butter and sugar; starting and ending with dry
Preheat oven to 350 °F
Liberally spray loaf pan with non stick cooking spray
Pour batter into prepared loaf pan, use an offset spatula to smooth the batter in the pan
Bake for 60 minutes, or until cake tester inserted in the center comes out clean
Remove from oven, allow pound cake to cool for 10 to 15 minutes before removing from pan
Transfer cake to a cooling rack to completely cool