Joy the Baker, and boy oh boy was she correct. My mom told me this was one of the tastiest things I've ever made.
Joy the Baker
For the Cake:
1 1/4 cups plus 1 Tablespoon brewed coffee
3/4 cup Dutch process cocoa powder
2 1/4 cups sugar
1 1/4 teaspoons kosher salt
2 1/2 teaspoons baking soda
2 whole eggs
1 egg yolk
1 1/4 cups plus 1 Tablespoon buttermilk
1 cup plus 2 Tablespoon canola oil
1 1/2 teaspoons vanilla extract
2 1/2 cups, plus 2 Tablespoons all-purpose flour, sifted
For the Glaze:
6 ounces unsweetened chocolate
3/4 cup unsalted butter
3 cups powdered sugar
1/2 cup sour cream, at room temperature
1/4 cup brewed coffee, cooled
Place an oven rack in the center of the oven and preheat to 350 degrees F.
Grease and flour a 10-inch Bundt pan and set aside.
To make the cake batter: Put brewed coffee and cocoa powder in a small saucepan and bring to a boil, whisking frequently. Remove from the heat and let come to room temperature.
In the bowl of a stand mixer fit with a whisk attachment, mix together sugar, salt, baking soda, eggs and egg yolk on low speed for about 1 minute. Add the buttermilk, oil and vanilla extract and mix on low again for another minute.
Add the flour and mix on medium speed for 2 minutes. Add the cooled cocoa mixture and mix on medium speed for 3 minutes. The batter will be very loose. Pour into the prepared cake pan and bake for 1 hour, or until a cake tester inserted in the cake comes out clean.
Let the cake cool completely in the pan and then invert onto a cooling rack.
To make the icing: Chop the chocolate into small pieces, put them in a heatproof bowl (or a double boiler), and set the bowl over a pot of barely simmering water. Be sure that the bottom of the bowl does not touch the boiling water. Remove the bowl from the heat when all of the chocolate bits have melted.
Melt the butter in a separate pan or in the microwave. Whisk the melted butter into the melted chocolate until thoroughly incorporated. Sift in half of the powdered sugar. Add the sour cream and whisk to combine. Sift in the remaining powdered sugar and whisk until smooth. The glaze should be thick and shiny. Lastly, add the coffee and whisk to create a glossy glaze.
Pour the glaze over the Bundt cake, covering it completely. Leave at room temperature until ready to serve.