To make the cake:

1. Preheat the oven to 350 degrees F and line a standard size (9 x 5) loaf pan with parchment paper. Grease any exposed insides with spray or butter. Set the prepared pan aside.
2. Add the orange juice and zest to a small saucepan and bring it to a low boil over medium heat. Simmer the juice and zest for 10-12 minutes, stirring occasionally, until it’s reduced by half and you have about 1/4 cup of juice.
3. Add the reduced orange juice/zest mixture to a 2 cup measuring cup along with the milk, eggs, sour cream, oil and vanilla extract. Stir everything together until well blended and smooth. Set the liquid aside while you prepare the dry ingredients and butter.
4. In the bowl of a stand mixer, sift the flour and baking powder together and whisk in the salt, brown sugar and granulated sugar until everything is evenly combined. There shouldn’t be any clumps of brown sugar remaining.
5. Add the unsalted butter to the flour and sugar mixture, and use the paddle attachment on medium speed to gradually incorporate the butter into the dry ingredients. After about a minute, the butter should have disappeared and the mixture should look like damp sand.
6. Reduce the mixer speed to low and slowly stream in the wet ingredients. Once everything has been mixed in, stop the mixer and scrape the sides and bottom of the bowl with a spatula. Gently fold in any remaining streaks/clumps of flour mixture until the batter is smooth. 
7. Add the batter to the prepared loaf pan and bake in the center rack of the oven for 48-56 minutes. The loaf should be slightly crested with a crack down the center, and a toothpick/cake tester should pull moist crumbs from the center of the loaf. If you see any raw batter on the toothpick, continue to bake the cake until it has completely set up.
8. Allow the cake to rest in the loaf pan for 15 minutes before removing to a wire rack. Cool the cake completely before frosting and serving.

To make the frosting:

1. Add the cream cheese, powdered sugar, salt and vanilla to a small saucepan and whisk over low heat until smooth and pourable. 
2. Pour frosting over cooled cake and allow to set up, which should take about 20 minutes. Once the frosting has set up, slice and serve!