Mimosa Cupcakes

Steps

1. 1Preheat oven to 350 degrees (F). Line (2) 12-cup muffin tins with paper cupcake liners, spray lightly with nonstick spray and set aside until needed.
2. 2In a large bowl sift together the flour, baking powder, baking soda, and salt. Set aside until needed.
3. 3Beat the butter, in the bowl of a stand mixer fitted with the paddle attachment or in large bowl and using a handheld electric mixer, until smooth and creamy, about 1 minute. Add in the sugar, a little bit at a time, and beat smooth. Once all of the sugar has been added, increase speed to medium-high and beat until light and fluffy, about 2 minutes, scraping down the sides and bottom of the bowl as needed.
4. 4Reduce speed to low. Add in the egg whites, a little bit at a time, beating well after each addition, and scraping down the sides and bottom of the bowl as needed. Turn mixer off.
5. 5In a spouted measuring cup, whisk together the orange zest, sour cream, orange juice, vanilla extract, and oil. Whisk until well combined.
6. 6With mixer on the lowest speed, add the flour in three additions, alternating with the sour cream mixture in two additions, beginning and ended with the flour, mixing until just combined.
7. 7Slowly pour in the champagne and mix until just combined.
8. 8Divide the cupcake batter evenly among the prepared pans, filling each mold 3/4 of the way full. Bake, one tray at a time, for 18 to 20 minutes, or until the cupcakes are domed, slightly golden, and a toothpick inserted in the center comes out clean.
9. 9Cool the cupcakes in the pan, on a wire cooling rack, for 10 minutes, before removing the cupcakes from the pan and placing on a cooling rack. Brush with champagne soaking syrup and set aside to cool completely before frosting.
10. 10For the Champagne Soaking Syrup: Stir the water and sugar together in a medium saucepan over medium heat until the sugar melts, then bring to a boil.
11. 11Remove the pan from heat and stir in the champagne. Pour the syrup into a heatproof bowl and set aside to cool.
12. 12Using a thin skewer, toothpick, or cake tester, poke holes all over the top of the cupcakes. Using a pastry brush, gently brush the the syrup on top of each cupcake, working slowly so that the cakes sops it up.
13. 13Allow cakes to cool completely before topping with the champagne frosting.
14. 14For the Champagne Frosting: In a large bowl using a handheld electric mixer, or in the bowl of a stand mixer fitted with the paddle attachment, beat the butter and cream cheese on medium-speed until smooth and creamy.
15. 15Reduce the speed to low and gradually add in the confectioners's sugar, beating until light and fluffy, about 2 minutes.
16. 16Add in the salt, champagne, and orange juice and beat smooth. If the consistency appears too thick, add a teaspoon of champagne or orange juice, but only if necessary. The frosting should be creamy and spreadable, but also thick enough to hold its shape.
17. 17Pipe or spread the frosting on top of each cooled cupcake. Then top with an orange slice and orange zest, if desired.