01 -  Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. 
 02 -  In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt. 
 03 -  In another bowl, beat together the softened butter, buttermilk, eggs, orange zest, vanilla extract, and orange juice until well combined. 
 04 -  Gradually add the wet ingredients to the dry ingredients, mixing until just combined. 
 05 -  Divide the batter evenly between the prepared cake pans and smooth the tops. 
 06 -  Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean. 
 07 -  Allow the cakes to cool in the pans for 10 minutes, then transfer to a wire rack to cool completely. 
 08 -  Beat the softened butter until creamy. Gradually add the powdered sugar, then mix in the orange juice and zest until smooth and fluffy. 
 09 -  Once the cakes are completely cooled, spread frosting between the layers and over the top and sides of the cake.