1tablespoon unsalted butter
3 1/2cups cake flour
1/2cup unsweetened cocoa (Dutch/natural)
1 1/2teaspoon salt
2cups canola oil
2 1/4cups granulated sugar
3large eggs
6tablespoons red food coloring
1 1/2teaspoon vanilla extract
1 1/4cup buttermilk
1 1/2teaspoon baking soda
1/2teaspoon baking powder
2 1/2teaspoons white vinegar
Icing
8ounces cream cheese, at room temperature
8ounces mascarpone cheese, at room temperature
1teaspoon pure vanilla extract
1cup confectioners/icing/powdered sugar, sifted
1 1/2cup cold heavy whipping cream (double cream, 35-40% butterfat)
1. 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.
2. 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.
3. Place the baking soda in a small bowl, stir in vinegar and add immediately to batter with machine running. Beat for 10 seconds.
4. 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.)
5. In the bowl of your electric stand mixer or with a hand mixer, at medium speed beat