Preheat the oven to 350 degrees F. Grease and flour a bundt cake pan. Place the flour, baking powder and salt in a bowl and whisk to combine. In another bowl, beat the butter and sugar together until lightened. Beat in the eggs, vanilla and orange zest. Mix in the dry ingredients alternately with the buttermilk and orange juice until just combined. Spoon the batter into the prepared pan. Bake for 35 to 40 minutes, or until a toothpick inserted into the centre of the cake pulls out clean. Unmould the cake onto a sided cake plate. Baste with 1/4 of the glaze. When it has soaked into the cake, brush with 1/4 more of the glaze. Repeat until all the glazed is used.