Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan. In a bowl, whisk the flour, baking powder, and salt.

In a large bowl, beat the butter and sugar with a hand mixer on medium speed until pale and fluffy, about 3 minutes.

Add the eggs one at a time, beating well after each, then mix in the orange zest, orange juice, and vanilla.

With the mixer on low, alternately add the flour mixture and buttermilk in three additions, starting and ending with flour. Mix just until combined.

Scrape the batter into the prepared pan and smooth the top. Bake 50 to 60 minutes, until a toothpick inserted in the center comes out with a few moist crumbs.

Cool the cake in the pan for 10 minutes, then transfer to a wire rack. Whisk the glaze ingredients until smooth and pour over the warm cake. Let the glaze set before slicing.