Step 1

Preheat oven to 350 degrees. Butter and flour two 8 1/2-by-4 1/2-by-2 1/2-inch loaf pans. Line bottoms with parchment or waxed paper. Sift together flour, baking powder, baking soda, and salt in a bowl; set aside. In another bowl, combine 1/4 cup orange juice, buttermilk, and vanilla; set aside.

Step 2

Cream butter and 2 cups sugar in the bowl of an electric mixer fitted with the paddle attachment until light and fluffy, about 5 minutes. Reduce mixer speed; add eggs, one at a time, combining well between each addition. Add orange zest; combine well. Add flour and buttermilk mixtures alternately to batter, beginning and ending with flour. Divide batter evenly between pans, smooth tops, and bake until golden brown and a cake tester comes out clean, 50 minutes to 1 hour.

Step 3

Meanwhile, combine remaining 1/4 cup orange juice and 1/4 cup sugar in a small saucepan. Cook over low heat until sugar dissolves. Cool cakes 10 minutes; transfer to a cooling rack over a baking tray. Spoon glaze over cakes; cool completely.

Step 4

Whisk together confectioners sugar and remaining 2 tablespoons orange juice in a small bowl until smooth. Drizzle over the top of one cake, and serve. Wrap other cake in plastic, and store in the refrigerator until needed.