Preheat an oven to 325°F. Lightly grease a round cake pan and dust with flour.

In a bowl, whisk together the flour, baking soda and salt until blended.

In the bowl of an electric mixer, beat together the butter, sugar, vanilla and orange and lemon zest on medium to medium-high speed until light and fluffy.

Add the eggs one at a time, beating well after each addition until just blended.

Sprinkle half of the flour mixture over the egg mixture and stir until both are just incorporated.

Stir in the sour cream, then sprinkle with the remaining flour mixture and stir until evenly distributed.

Pour the batter into the prepared pan and tap gently on the counter to even out and settle the ingredients.

Bake until a toothpick inserted into the center comes out clean, about 70 minutes, or longer if using a metal pan.

Transfer the pan to a wire rack and let cool for 15 minutes.

Run a thin knife around the inside of the pan, invert the cake onto the rack and lift off the pan.

Place the cake on one of its sides and continue cooling.

Once cooled cut the cake in half, frost the middle, place the top on the cake, frost entirely (it may take two layers...one crumb layer and then a final of frosting).

In the bowl of an electric mixer fitted with the flat beater, combine the confectioners’ sugar, butter, the 4 ½ Tbs. orange juice, the vanilla and salt and beat on low speed until combined, about 1 minute.

Stop the mixer and scrape down the sides of the bowl.

Increase the speed to medium and beat until fluffy, about 3 minutes.