Place the orange zest into a saucepan and add water to cover; bring to a boil and cook 5 minutes. Strain the zest through a mesh strainer and return to the saucepan along with 1/2 cup white sugar and 1/4 cup of water. Return to a boil, then reduce heat to medium-low; cook, stirring constantly, until the water has evaporated. Allow to cool until lukewarm.
Preheat an oven to 350 degrees F (175 degrees C). Grease and flour a 9x5 inch loaf pan.
Whisk the flour, baking powder, and salt together in a bowl; set aside. Whisk the egg and 1 cup of sugar in a bowl. Stir in the butter, milk, and cooled orange zest until blended; stir in the flour mixture until just moistened then pour into the prepared loaf pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 55 to 65 minutes. Cool in the pan for 10 minutes before removing to cool completely on a wire rack.
