Grease & flour a standard (8.5 x 4.5 inch) loaf pan. You could also spray it with baking spray, or use my baking spray replacement (linked in the post).
Zest and juice your orange. You will need about 2 Tb of orange zest and a total of about 1/4 c orange juice (for the cake and the glaze.) Set those aside for now.
In a bowl, combine the flour, baking powder, baking soda, and salt. Give them a quick stir and set it aside for now.
In your mixing bowl, beat the butter until it is fluffy.
Mix in the sugar and eggs until creamy.
Add in the vanilla extract.
Mix in half of your dry ingredients.
Mix in the buttermilk.
Mix in the remaining dry ingredients.
Mix in 2 Tb orange juice.
Stir in the orange zest, making sure to scrape the bowl with a rubber spatula to get everything combined well.
Spread the cake batter in your prepared loaf pan.
Bake the cake for 50-60 minutes, or until it tests done in the center with a toothpick.
Remove the cake to a cooling rack and let the cake cool a couple minutes in the pan.
Slide a knife around the sides of the pan and transfer the cake to the cooling rack to allow it to cool completely.
Prepare the Glaze:
Combine the powdered sugar, vanilla extract, and a teaspoon or two of orange juice. Whisk these together until smooth. Add just enough juice to make the glaze able to be drizzled.
Drizzle the cooled cake with the glaze.
If you wish to have a thicker glaze, more like a frosting, you can add more powdered sugar or use less juice if you like.
Video
Notes
Alternative Glaze: For a different glaze, combine 1/4 c granulated sugar, 1/4 c orange juice, and 1/2 teaspoon vanilla extract in a sauce pan. Simmer it together until the sugar is dissolved and drizzle this over the cake while it is still warm.