Pre-heat oven to 350 degrees. Liberally grease then flour all of the nooks and crannies of a Bundt pan and set aside.
Sift together the dry ingredients and set aside.
In the bowl of a stand mixer, beat the butter with the paddle attachment on medium speed until smooth. Meanwhile, rub the citrus zest into the sugar with your fingertips until fragrant. Add the sugar (and zest) to the butter and cream together on medium-low until light and fluffy, 3 to 4 minutes).
Stop the mixer and scrape down the bowl. With the mixer on low, add in the eggs and yolk – one at a time. Add in the oil and mix until combined. Stop the mixer and scrape down the bow.
With the mixer on low, carefully add in the half of the dry ingredients. Once combined, add in the sour cream, milk, and orange juice.
Add in the remaining dry ingredients and mix on medium-low until the last bits of flour are incorporated.
Pour the batter into the prepared pan. Bake for 45 to 55 minutes, until a thin knife inserted into the center comes out clean.
Cool for only 10 to 15 minutes – or until just cool enough to lift the pan without burning your fingertips. Place a cooling rack or cutting board on top of the cake (the bottom) and flip the cake pan right-side up to unmold the cake. The cake should still be warm or it may stick to the pan if cooled for too long. Loosen the edges gently with a flexible rubber spatula, but refrain from running a knife around the edges or you may cut into the sides of the decorative cake.