1. Preheat oven to 350°F (176°C) and prepare a cupcake pan with cupcake liners.
2. In a large mixing bowl, cream the butter and sugar together until light in color and fluffy, about 3-4 minutes. Do not skimp on the amount of creaming time.
3. Add sour cream, vanilla extract and orange zest and mix until well combined.
4. Add egg whites in two batches, mixing until well combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
5. Combine dry ingredients in a separate bowl, then combine the milk, water and orange juice in a small measuring cup.
6. Add half of the dry ingredients to the batter and mix until well combined. Add the milk mixture and mix until well combined. Add remaining dry ingredients and mix until well combined. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated. Do not over mix.
7. Fill the cupcake liners a little more than halfway. Bake for 15-17 minutes, or until a toothpick inserted comes out with a few crumbs.
8. Remove cupcakes from oven and allow to cool for 2-3 minutes, then remove to cooling rack to finish cooling.
9. When the cupcakes are cooled, make the filling. Add the heavy whipping cream, powdered sugar and vanilla extract to a large mixer bowl and whip on high speed until soft peaks begin to form.
10. Add the cream cheese and continue whipping until stiff peaks form.
11. Remove the centers of the cupcakes using a cupcake corer or sharp knife, then fill with the cream filling.
To make the frosting, beat the butter in a large mixer bowl until smooth.
11. Add 2 cups of powdered sugar and mix until smooth.
12. Add the orange zest and 1 tablespoon of orange juice and mix until smooth.
13. Add the remaining powdered sugar and mix until smooth.
14. Add the remaining orange juice as needed for the right consistency of frosting and mix until smooth.
15. Color the frosting as desired, then pipe the frosting onto the cupcakes. I used Ateco tip 844.
16. Decorate the cupcakes with orange slices, or your preferred decorations.