Preheat the oven to 350 degrees, then grease your loaf pans or mini loaf pans.
In a large bowl, add the orange zest and granulated sugar. Mix them really well, grinding the zest into the sugar. The mixture will start to turn orange, and you'll start to really smell the orange flavor.
Add the flour, baking powder, and salt to the sugar mixture, then combine well. Set aside.
In another bowl, whisk together the buttermilk, butter, eggs, vanilla, and orange juice. Mix well, then add to the flour mixture, stirring only until combined.
Pour the batter into your prepared pans, and bake until a toothpick comes out clean--about 70 minutes for a full loaf, and 45-50 minutes for a mini loaf. If you're using a different sized pan, alter your times appropriately and watch closely. If the top is getting too brown before it's done, cover with foil for the last 5-10 minutes.
When the bread is finished, remove from the oven and let cool 30 minutes before taking the bread out of the pan. If I'm using disposable mini loaf pans, I don't remove the bread--since that's how I'm giving it. Just pour the glaze over the top before wrapping them up.
Make the glaze, then drizzle it over the warm bread.