Preheat the oven to 325 degrees, and grease three 9″ round cake pans with baking spray. Set aside.
Separate egg yolks from egg whites, allowing egg whites to stand at room temperature for 30 minutes (it’s easier to separate the eggs when cold, but it is better to whip the egg whites when they are at room temperature). Set aside.
With a mixer, beat butter until fluffy, about 1 minute. Add in oil, beating until well combined. Add in sugar, 1 cup at a time, mixing until well combined, about 1 minute. Add in egg yolks, one at a time, beating well after each addition.
In a separate bowl, sift together flour, corn starch, baking powder, baking soda, and salt. Set aside.
Mix together vanilla extract, milk, sour cream, and orange zest.
Alternately, mix the dry ingredients and wet ingredients with the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.
Beat egg whites until stiff peaks form, about 1-2 minutes. Gently fold egg whites into the batter until it combined.
Toss cranberries with flour (this helps keep the cranberries from sinking to the bottom of the batter) and gently fold them into the batter.
Divide the batter evenly between the three cake pans. Bake for 20-25 minutes, or until a cake tester comes out clean. Allow to cool completely before frosting.
Frosting
Beat butter and cream cheese until well combined, about 1-2 minutes. Add in orange zest and vanilla extract, mixing until combined. Add in powdered sugar, 1 cup at a time, starting with 4 cups. Scrape down the sides of the bowl as needed, and mix until combined. Add in orange juice, 1 Tbsp at a time, beginning with 2 Tbsp.
If the frosting is too thin, add in the last cup of powdered sugar. If the frosting is too thick, add in the last Tbsp of orange juice. Once it has reached your desired consistency, add in a pinch of salt (this helps balance out the sweetness).
Assembly
Set the bottom cake layer on a cake stand or plate. Spread the top with 1/2 cup of frosting, reaching the frosting the edge of the cake. Top with the middle layer, and repeat the process. Place the final layer on top, and spread the remaining frosting over the top and sides of the cake.
