Preheat the oven to 350ºF and prepare three 6-inch cake pans by spraying the sides with cooking spray and placing a wax or parchment paper circle into the bottom of each one. Mix together the orange juice and whole milk and set aside. Measure the cake flour by spooning into your measuring cup and leveling it. Place it into a medium sized bowl and add the baking powder, baking soda, and salt. Whisk together and set aside.

In the bowl of your stand mixer (a handheld mixer works fine too!), cream the butter on high for two minutes until it's light and fluffy. Add in white granulated sugar and continue to mix on medium-high for another two minutes, scraping down the bowl and paddle as needed. Add the eggs one at a time. Add the orange zest, sour cream, vanilla, and orange food coloring (if using) and mix for one minute on medium-high, scraping down the bowl and paddle once more. It will look curdled at this point, but that is ok!

With the mixer on low speed, add in the dry ingredients and mix until just combined. Add the whole milk and orange juice mixture in a steady stream and mix until just incorporated. Scrape down the sides and bottom of the bowl and give it a few stirs to make sure there are no lumps.

Pour batter evenly between the cake pans and bake for 25-30 minutes, until a toothpick inserted comes out clean. Cool the cakes in the pan for ten minutes before removing and continuing to cool on a wire rack or flat surface.

With a hand mixer or paddle attachment on your stand mixer, cream the butter on medium-high until creamy and light (almost white) in color. About 7 minutes.

With the mixer on low, add the powdered sugar a few cups at a time, scraping down after each addition and making sure each addition is fully incorporated before adding the next one.

Add the whole milk, vanilla, and salt and mix on low for another minute or two until fully incorporated.

After the cakes have cooled completely, torte each layer to the desired height, then fill and crumb coat the cake with vanilla buttercream. To create the look pictured, use this watercolor cake tutorial with orange food coloring to create a watercolor finish, then top with a white chocolate ganache half drip and pipe a simple border on top with Wilton Tip 6B.