Cake recipe adapted from Deb Perelman's Smitten Kitchen, originally from “The Confetti Cakes Cookbook” by Elisa Strauss via the New York Times 2/14/07.
Yields 9-inch round 3 cake layers OR one 9x13 inch sheet cake and 12 cupcakes. —pickyin
Preheat oven to 350°F/180°C. Grease a 9x13x1 inch baking sheet or jelly roll pan and line the bottom with parchment. Line a 12-cup standard muffin tin with cupcake liners. Whisk cake flour, cocoa and salt in a bowl.
Place oil and sugar in bowl of an electric stand mixer and beat at medium speed until well-blended. Beat in eggs one at a time. With machine on low, very slowly add red food coloring. Take care, the batter may splash. Add in the vanilla. Add the flour mixture alternately with buttermilk in two batches (starting and ending with the flour). Scrape down bowl and beat just long enough to combine.
Place the baking soda in a small bowl, stir in vinegar and add immediately to batter with machine running. Beat for 10 seconds.
Divide 2/3 of the batter onto the baking sheet and the rest into the muffin tin. Place in oven and bake until a cake tester comes out clean, 15 to 20 minutes each for the sheet cake and cupcakes. Let cool in pans for at least 20 minutes. Remove the sheet cake from the pan by flipping it over and peel off the parchment. Trim of the curved sides if necessary (doing this will yield an 8x12 inch sheet) and divide the cake along the longer side into three 8x4 inch portions. Cool completely cakes completely before frosting. (I froze the sheets for two hours before icing.)
In the bowl of your electric stand mixer or with a hand mixer, at medium speed beat the cream cheese and mascarpone cheese until smooth. Add in the vanilla and icing sugar and beat until smooth. Using the whisk attachment, gradually add in the heavy cream and whip at increasing speed until the frosting is thick enough to spread. Be careful not to overwhip or you'll end up with mascarpone butter. If necessary, add more sugar or cream as needed to get the right consistency. Chill to thicken before using.
To assemble the cake, remove the layers from the freezer and frost each layers with about 4 tablespoons of cream in between each layer. Spread a thin layer of frosting over the entire cake with a crumb coat and freeze uncovered for 45 minutes to an hour. Repeat with a second crumb coat if necessary before frosting the final coating. Decorate accordingly, I used some cocoa nibs on the sides and top of this cake. I find that refrigerating the frosted cake overnight keeps the frosting stable at room temperature for many hours when the cake was served the next day. Cakes keeps covered and chilled for up to 3 days.