1 ½cupsunsalted butter, at room temperature(3 sticks)
2tablespoonchampagne reduction
Instructions
For Cake:
Preheat oven to 350F. Spray muffin pans with nonstick spray or line with paper liners. Set aside.
In a small bowl, combine the dry ingredients (cake flour, baking powder, baking soda, and salt. Set aside.
In the bowl of a stand mixer, beat butter and sugar until light and fluffy. Scrape down the sides of the bowl.
Add egg whites and vanilla, beating to combine. Scrape down the sides of the bowl.
Add orange zest and sour cream. Beat to combine. Scrape down the sides of the bowl (seeing a trend here?).
Add dry ingredients, mixing just until incorporated. With the mixer on low speed, slowly add the orange juice and champagne, mixing until just combined.
Divide the batter between the muffin cups, filling each about ⅔ full. Bake 18-20 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool 10 minutes in the pan, then remove and allow to cool completely on a wire rack.
For Champagne Reduction:
Pour champagne into a small saucepan. Over medium-high heat, reduce champagne to about 2 tablespoons in volume. Reduction will be syrupy (see note).
For Buttercream:
Put egg whites in the bowl of a stand mixer, taking care to ensure no yolk is in the bowl (see note).
In a small saucepan, combine water and /2 cup sugar. Stir to moisten sugar, and do not stir after that (see note). Warm over low heat until sugar dissolves.
Once sugar is dissolved, increase heat to medium-high. Cook until syrup reaches 246F-250F.
When syrup reaches 240F, begin beating the egg whites using the whisk attachment. Once frothy, add cream of tartar and remaining 2 tablespoons sugar. Beat on high until stiff peaks form.The goal is for the egg whites to reach stiff peaks at the same time the syrup reaches temperature. If the egg whites are done early, let the mixer run on low speed until the syrup comes to temperature.
Once syrup is to temperature, remove from the heat. With the mixer running on low speed, carefully pour the syrup into the egg whites in a slow, steady stream (see note).
Beat mixture on medium-high until the bottom of the bowl is no longer warm to the touch. Then add butter, 2-3 tablespoons at a time, allowing the butter to incorporate completely after each addition.
With mixer on low, drizzle in champagne reduction. Beat to combine.
Top cupcakes with buttercream.Enjoy!
Notes
Note on cake flour: You can choose to use all-purpose flour for this recipe if that's all you've got on-hand, but cake flour will result in a lighter, fluffier cake. If you can't find cake flour at your local grocery store, you can find it [here].Note on champagne reduction: You want to reduce the champagne so that you can flavor the buttercream without adding too much liquid. The more liquid you add, the less likely it will combine with the buttercream. In order for the flavor to come through, the reduction is necessary to add the concentrated flavor of the champagne without having to add a lot of liquid.Note on egg whites: Egg whites need to be *completely* free of yolk! Make sure your bowl is squeaky clean, too. Even a drop of fat will keep your egg whites from whipping up properly. If you get yolk in your whites, dump it out, wash the bowl, and start over.Note on stirring sugar syrup: Stirring the sugar syrup promotes crystallization of the sugar, when that's the opposite of what you want. Don't stir, even though (like me) you really want to.Note on handling hot sugar syrup: Don't worry about scraping out the saucepan to get every last bit of syrup. Keep your focus on not burning yourself. Be VERY careful not to touch the syrup, as it will stick to your skin and could cause serious burns!Piping Buttercream: You can spread the buttercream with a knife or dollop it on top with a spoon if you'd like. I piped the buttercream with a 1M tip, like this one [here].