Preheat the oven to 325°F.
Prepare the bundt pan by buttering the inside lightly with softened butter. Make sure the pan is evenly coated and that the butter has reached all the nooks and crannies. Dust the inside with flour, tapping out the excess. Set the pan aside for later.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In the bowl of a mixer fitted with the paddle attachment, cream the butter, the sugar, and the orange zest for at least 5 minutes until it is light and fluffy. Add in the eggs, one at a time, mixing well between each addition. The batter should be very light and fluffy at this point.
Add the sour cream and vanilla, and beat again to mix it really well.
Add half the dry ingredients and stir on low to incorporate. Mix in the orange juice, and then the rest of the flour. Don't mix it in completely. When there's still some flour not yet incorporated, finish stirring with a spatula or a big wooden spoon, being sure to scrape up what's stuck to the bottom of the bowl. Fold in the cranberries.
Dollop the batter into the prepared pan and swirl and smooth it with a small offset spatula. Bang the pan on the counter several times to make sure the batter settles into all the grooves of the pan. If you are worried, you can even push a knife through the batter to force it into place.
Bake the bundt until it's golden brown on the top and edges. Insert a cake tester or long skewer to check the cake is done in the middle (it should come out clean). It takes about 90 minutes to bake completely and I recommend rotating the pan after about 75 minutes to make sure the front and back bake evenly. Let the bundt cool for about 20 minutes in the pan before inverting on a wire rack to cool completely.