Preheat the oven to 350 degrees. Prepare two loaf pans with nonstick cooking spray.
In a medium bowl, whisk together the flour, baking powder, and salt. Sset aside.
In a mixing bowl, beat the butter and sugar until fluffy, about 7 minutes, scraping down the sides as needed.
Next, add the eggs one at a time, beating well between each addition and scraping down the sides as needed. Mix in the orange zest and vanilla.
To the batter, add half of the flour and beat until combined. Mix in the sour cream until blended and then the remaining flour, occasionally scraping down the sides.
Transfer the batter to the prepared pans.
Bake for 45 to 60 minutes or until a toothpick inserted in the center returns clean.
Cool the pans on a wire rack for 10 minutes prior to removing the loaves to cool completely on the wire rack.
Dust with powdered sugar, if desired, prior to slicing and serving.