Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. In a large mixing bowl, combine the flour, baking powder, baking soda, and salt. Set aside. In another bowl, cream the butter and sugar until light and fluffy. Add the eggs one at a time, beating well after each addition.

Mix in the vanilla extract and orange zest. Alternately add the dry ingredients and the orange juice and buttermilk to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.

Divide the batter evenly between the prepared cake pans. Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean. Allow the cakes to cool in the pans for 10 minutes, then turn them out onto a wire rack to cool completely.

In a mixing bowl, beat the butter until creamy. Gradually add the powdered sugar, mixing well. Stir in the vanilla extract, orange juice, and orange zest. Add heavy cream as needed to achieve the desired consistency.

Once the cakes are completely cool, place one layer on a serving plate. Spread a generous amount of frosting on top. Place the second layer on top and spread frosting over the top and sides of the cake.

Decorate with optional garnishes such as orange slices, mint leaves, or edible flowers for added visual appeal. Slice and serve.

Store the cake in an airtight container in the refrigerator for up to 4 days. Allow to come to room temperature before serving for the best texture and flavor.