Preheat the oven to 350°F. Line the bottom of 2 9-inch round pans with a round of parchment paper. Spray the top with cocoa powder. Set aside.
In a large bowl, mix together the flour, sugar, cocoa powder, baking powder, baking soda and salt. Mix in the eggs, oil and orange juice until fully incorporated.
Divide the batter into the prepared baking pans. Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted comes out clean. Refrigerate the cakes to make them easier to frost.
In the bowl of a stand mixer, cream together the butter and vanilla until light and creamy. Mix in the powdered sugar and the orange juice until smooth. Frost the cake, as desired.
Notes
I use avocado oil, but any neutral oil works well.