1 cup + 2 tablespoons gluten free flour
1/2 teaspoon xanthan gum (omit if your blend already contains it)
11 tablespoons unsweetened cocoa powder
3/8 teaspoon kosher salt
3/8 teaspoon baking soda
3/4 cup sugar
1/2 cup + 1 tablespoon sour cream, at room temperature
6 tablespoons vegetable oil
1 egg + 1 egg yolk (out of shell) at room temperature, beaten
1/2 cup + 1 TBSP warm water (about 95°F)
1/4 cup unsweetened cocoa powder
1/2 cup warm water
10 ounces dark chocolate, chopped
4 tablespoons unsalted butter, chopped
2 cups heavy whipping cream
1/4 cup confectioners’ sugar
HOW TO PREPARE:
Preheat your oven to 350°F. Grease an 8-inch round springform baking pan and set it aside.
Make the cake. In a large bowl, place the flour, xanthan gum, cocoa powder, salt, baking soda and sugar, and whisk to combine well. Create a well in the center of the dry ingredients and add the sour cream, oil, eggs and water, mixing to combine after each addition. The batter should be very thickly pourable. Scrape the batter into the prepared pan, smooth into an even layer and place in the center of the preheated oven. Bake until a toothpick inserted in the center of the cake comes out mostly clean or with a few moist crumbs attached (about 30 minutes). Do not overbake. Remove from the oven and allow to cool for 10 minutes in the pan before inverting onto a wire rack to cool completely.
While the cake is cooling, make the chocolate mousse. In a small bowl, whisk the cocoa powder into the warm water until it dissolves completely. Set it aside. In a small, heat-safe bowl, place the chopped chocolate and chopped butter, and place over a small saucepan of simmering water, making sure the bowl does not touch the water. Melt the chocolate and butter over the simmering water, stirring occasionally, until smooth. Alternatively, you can melt them together in the microwave in short, 30-second bursts, stirring well in between. Remove the melted chocolate and butter, and whisk the cocoa powder dissolved in water into it until smooth. Set the bowl aside. In the bowl of a stand mixer fitted with the whisk attachment, or in a large bowl with a hand mixer, whip the heavy whipping cream on medium-high speed until soft peaks form. Add the confectioners’ sugar, and whip again until stiff, shiny peaks form. Pour the chocolate mixture into the bowl of whipped cream slowly, carefully folding the ingredients together and taking care not to deflate the whipped cream more than necessary. Fold until no white streaks remain.
Assemble the cake. Spoon the chocolate mousse onto the cake, and smooth the top. Refrigerate the cake until the chocolate mousse is set (about 2 hours). Slice and serve chilled.