Preheat oven to 325°F.
In a medium bowl, combine the flour, baking powder and salt. Set aside
In the bowl of an electric mixer, using the whisk attachment, cream together the butter, sugar and orange zest on medium low speed for two minutes until fluffy. Stop halfway through to scrape the sides of the bowl with a rubber spatula. Be sure there are no clumps of unmixed butter.
Add the eggs one at a time, mixing after each addition.
Add the sour cream, orange juice and vanilla. Mix until combined. (Mixture may separate a bit, but it will come together when flour is added)
On low speed, slowly add the flour mixture and mix until just combined. Stop the mixer, scrape the sides and bottom of the bowl with a rubber spatula and mix for another 10 seconds. Try to avoid over-mixing.
Generously grease the loaf pans generously with nonstick spray. This recipe makes either 2, 8-inch loaves or 5 mini loaves. Spoon the batter into the pans, filling no more than two-thirds full.
For 8-inch loaves, bake for 50-60 minutes, or until an inserted toothpick comes out clean. Mini loaf sizes will need less bake time (closer to 45-50 minutes). All ovens bake differently so be sure to keep an eye on it.
Let the orange pound cake cool in the pans for 20 minutes before removing and cooling completely on a wire rack.
Prepare the orange zest glaze by combining the powdered sugar, milk and orange zest. Add more powdered sugar or milk to get a thick consistency.
Drizzle over loaves after they have completely cooled. The glaze should set up and harden in about 20 minutes. Enjoy!