Heat oven to 350 degrees.  Spray butter spray on bottom of two bread loaf pans (8 ½ x 4 ½ x 2 ½ in).  Line the bottoms of pans with parchment paper.

Cream butter and 2 cups of the granulated sugar in bowl of electric mixer fitted with the paddle attachment for about 5 minutes, or until light and fluffy.  With mixer on medium speed, beat the eggs, one at a time, then mix in orange zest.

In large bowl, sift together flour, baking powder, baking soda, and salt.  In another bowl, combine ¼ cup of orange juice, buttermilk, and vanilla.  Add the flour and buttermilk mixtures alternately to the batter, beginning and ending with the flour.

Divide the batter evenly between the pans, smooth the tops, and bake for 45 minutes to 1 hour, until a toothpick inserted in center comes out clean.

While cakes bake, in a medium saucepan, cook the remaining ½ cup of granulated sugar with the remaining ½ cup orange juice over low heat, until sugar dissolves.

When the cakes are done, let them cool for 10 minutes.  Take them out of the pans and place them on a baking rack set over a tray.  Spoon the orange syrup over the cakes and allow the cakes to cool completely.

For the glaze, stir together the confectioner's sugar and orange juice in a bowl, mixing with a wire whisk, until smooth.  Add a few more drops of juice, if necessary, to make it pour easily.  Pour over the top of each cake and allow the glaze to dry.