Preheat the oven to 350F (180C) and grease one 10, or 12 cups bundt pan.
In a medium bowl mix the flour and baking powder.
Mix the sour cream, orange juice, and vanilla extract in a measuring cup.
Rub the zest into the sugar using a fork or your fingers in a large bowl, or a bowl of a standing mixer fitted with the paddle attchment.
Add the butter to the sugar and mix for 4-5 minutes, until light and airy. Scrape the sides and bottom of the bowl.
Add the eggs, one at a time waiting for each egg to completely incorporate before adding the next.
With the mixer on low speed, add the flour mixture in three additions alternating with the wet ingredients. Starting and finishing with the dry ingredients.
Fill the prepared pan with the cake batter and bake for 40-45 minutes, or until a toothpick comes out with a few moist crumbs from the center of the cake.
Remove from the oven and allow the cake to cool in the pan for 35-40 minutes, or until the pan is cool enough to hold with your hands (but still warm).