Preheat oven to 350℉. Grease a 13x9-inch baking dish with cooking spray. Set aside.
For the Brownies: Cream the butter and sugar with an electric mixer. Add the eggs and mix well. Scrape bowl. Add the orange zest and juice. Mix until incorporated.
Add the flour and salt. Mix until just combined. Spread batter evenly into the prepared pan.
Bake at 350℉ for 25 to 30 minutes, until a toothpick comes out clean from the center. The top and edges will be lightly browned.
Make the Frosting: In a large bowl with an electric hand mixer, beat the cream cheese and butter until smooth. Add the orange zest, 1 Tbsp of orange juice, and the powdered sugar. Mix until incorporated. Add up to 1 Tbsp more orange juice if needed, depending on desired taste/consistency.
Pierce the entire sheet of brownies with a fork while still warm. Spread frosting over the top. Refrigerate until cool. Then cut and serve. Keep leftovers refrigerated.
Notes
You will need a total of 2-3 fresh oranges for juice and zest needed for this recipe.