Preheat the oven to 325 F. Grease and flour two 8” cake pans.
Set the butter in the bowl of a stand mixer fitted with the paddle attachment, then zest the orange over the butter and turn the mixer on. Pour in the sugar and beat until creamed, very light and fluffy, about 5 full minutes.
Add the salt and vanilla and beat to combine. Add the eggs, one at a time, allowing each to be almost fully combined before adding another. Use a rubber spatula to scrape the bottom of the bowl and ensure everything is well mixed.
Sift in the cake flour with the baking soda and powder then use the rubber spatula to fold it in gently. Turn the mixer on low and slowly pour in the buttermilk and orange juice. Mix to combine.
Divide the batter between the two cake pans and bake for 30-40 minutes until a cake tester comes out clean or you can press the top and it bounces back. Let cool in the pan for a few minutes then set on a cooling rack. If the cakes have a light dome, use a serrated bread knife to slice them off. Let cool completely.