FOR THE CAKE/CUPCAKES
1 3/4 cup (245 g) basic gum-free gluten free flour (162 g superfine white rice flour + 54 g potato starch + 29 g tapioca starch/flour)
1/4 teaspoon xanthan gum
2 tablespoons (18 g) cornstarch (can’t have cornstarch? try arrowroot and let us know how it goes!)
1 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon kosher salt
1 cup (200 g) granulated sugar
1 egg (60 g, out of shell), separated + 1 egg white, at room temperature
8 tablespoons (112 g) unsalted butter, at room temperature
2/3 cup (5 1/3 fluid ounces) sparkling wine (can substitute ginger ale for an alcohol-free version)
FOR CHAMPAGNE FROSTING
1 1/2 cups (300 g) granulated sugar
1/2 teaspoon cream of tartar
1/4 cup sparkling wine (can substitute ginger ale for an alcohol-free version)
5 egg whites (150 g total)
24 tablespoons (336 g) unsalted butter, cubed and kept cool (but not cold)
1/8 teaspoon kosher salt
First, make the cake or cupcakes. Preheat your oven to 350°F. If making a cake, grease a 9-inch round baking pan and set it aside. If making cupcakes, grease or line the wells of a standard 12-cup muffin tin and set it aside.
In a large bowl, place the gum-free flour blend, xanthan gum, cornstarch, baking powder, baking soda, salt and 3/4 cup (150 g) of the granulated sugar, and whisk to combine well. Set the bowl of dry ingredients aside. In the bowl of a stand mixer fitted with the whisk attachment, or a large bowl with a hand mixer, place the 2 egg whites and beat on medium speed until soft peaks form. Add the remaining 1/4 cup (50 g) granulated sugar, and beat again on medium speed until stiff (but not dry) peaks form. Still using the whisk attachment, beat in the egg yolk and butter on medium speed. The mixture will be thick and the egg whites will deflate a bit, but the mixture will still be fluffy. Add the dry ingredients and the sparkling wine, alternating one and then the other, and beginning and ending with the dry ingredients. Mix until just combined. The batter will be pale yellow and fluffy.
If making a cake, transfer the batter to the prepared baking pan and spread and shake into an even layer. If making cupcakes, divide the batter evenly among the 12 muffin tins (filling them about 3/4 of the way full). Place the cake or cupcakes in the center of the preheated oven and bake until pale golden and a toothpick inserted in the center comes out clean (about 19 minutes for cupcakes, 25 minutes for a cake). Remove the cake or cupcakes from the oven and allow to cool in the pan for at least 10 minutes before transferring a wire rack to cool completely.
While the cake or cupcakes are cooling, make the frosting. Clean the bowl of your stand mixer, place the sugar, cream of tartar, and sparkling wine and egg whites, and whisk to combine well. Place the bowl over a pot of simmering water and clip a candy thermometer to the side of the bowl, making sure the tip of the thermometer is in the liquid and not on the bottom of the bowl or you will get an inaccurate reading. The bowl should be just above the simmering (but not boiling water) without touching it. Cook the sugar mixture, stirring occasionally, until it reaches 160°F. Remove the bowl from the heat, and place it in the stand mixer. Beat, with the whisk attachment for about 7 minutes or until the mixture is white, glossy and thick (and about tripled in size). Right now, this is your 7-minute frosting, and it can be used as is to frost your cooled cake or cupcakes. If you would like to make swiss meringue buttercream, continue with the next step.
To make swiss meringue buttercream from your 7-minute frosting, once the side of the mixing bowl is cool to the touch on the outside of the bowl, switch to the paddle attachment and begin adding the cubed, cool butter while the mixer is on medium speed. Continue to beat until all of the butter is added and the mixture is silky smooth and thick. If the mixture looks curdled, continue to beat for a while longer until the butter is smooth (the “curdles” are actually butter that is too cold). If the mixture is runny, place the bowl in the refrigerator for 15 minutes and beat again. Add the salt, and beat to combine.
Frost the cake or cupcakes with the champagne frosting as desired, and serve.
P.S. Do you have your copy of Bakes Bread yet? Now that the holidays have (mostly) come and gone, it’s time to get that bread in the oven!