Preheat the oven to 350°F (175°C). Grease and flour two 9 x 5-inch loaf pans. Line the bottoms with parchment paper for easier removal.

In a stand mixer fitted with the paddle attachment, cream the butter and sugar together on medium speed until light and fluffy, approximately 5 minutes.

With the mixer running, add the eggs one at a time, ensuring each is fully incorporated before adding the next. Add the orange zest and mix to combine.

In a large mixing bowl, sift together the flour, baking powder, baking soda, and salt. In a separate bowl, combine the orange juice, buttermilk, and vanilla extract.

Alternately add the flour mixture and buttermilk mixture to the creamed butter, beginning and ending with the flour. Mix until just combined. Do not overmix.

Evenly divide the batter between the two prepared pans. Smooth the tops and bake for 40 to 50 minutes, or until a toothpick inserted in the center comes out clean.

While the cakes are baking, combine the orange juice and sugar in a small saucepan over medium heat. Stir until the sugar dissolves completely. Simmer for an additional 3 minutes and then remove from heat.

Once the cakes are out of the oven, allow them to cool in their pans for 10 minutes. Carefully transfer them to a wire rack placed over a baking sheet. Use a toothpick to gently poke holes in the tops and sides, then brush generously with the prepared syrup. Repeat once more after the syrup is absorbed.

In a medium bowl, whisk together the sifted confectioners’ sugar and 4 tablespoons of orange juice. Add more juice, one tablespoon at a time, until the glaze reaches a thick but pourable consistency. Drizzle the glaze over the cooled loaves and allow it to set for at least 15 minutes before serving.