1/2cupfreshly squeezed orange juicefrom about 2 oranges
4cupsicing sugar(confectioner's or powdered sugar)
Preheat the oven to 350 degrees F. Grease and flour 2 8-inch cake pans.
In a medium bowl, whisk together the flour, baking powder and salt.
In a stand mixer fitted with the paddle attachment, cream together the butter, oil and sugar on medium speed until light and fluffy, about 3-4 minutes.
To the stand mixer bowl, add the eggs, egg yolk, vanilla and orange zest. Beat until well combined, scraping down the sides of the bowl as needed.
In a measuring cup, combine the milk and orange juice.
With the mixer on low speed, alternate adding the flour mixture and milk/OJ mixture, in 3 instalments each, beating until JUST combined (do not over beat).
Remove the bowl from the stand mixer and give it a good stir with a rubber spatula, scraping the bottom and sides of the bowl. Divide the batter evenly between the prepared cake pans and bake for 30-35 minutes until a toothpick inserted in the center comes out clean.
Allow the layers to cool in the pan for 15-20 minutes and turn them over onto a cooling rack to cool completely.
In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter and cream cheese on medium speed until smooth. Beat in the vanilla extract and orange zest.
Add the confectioner's sugar, one cup at a time, until the frosting is smooth and creamy. If you think it is too soft, put the bowl in the refrigerator for about an hour to firm up.
Place one cake layer on a plate or turntable, and using an offset spatula, frost the top with about 1 cup of frosting. Place the second layer upside down on top and frost the top and sides of the cake. Decorate with orange slices if desired.
Due to the fresh ingredients used in the frosting, and because cream cheese frosting has a tendency to get soft at room temperature, this cake is best stored in the refrigerator. Take it out 15 minutes or so before serving.