Cake Batter
1 3/4 cups cake flour
3/4 cup unsweetened cocoa powder (William Sonoma)
1 1/2 teaspoons baking soda
1/2 teaspoon salt
1 3/3 cups sugar
2 cups of sour cream
1/3 cup of unsalted butter (softened)
2 large eggs
1 teaspoon pure vanilla extract

Fudge Frosting
5 1/2 ounces of unsweetened chocolate
1 1/3 cups of sugar
1 cup of whipping cream
1/2 cup (one stick) of unsalted butter, softened
1 tablespoon of pure vanilla extract

Cake Batter
1. Fifteen minutes before baking, place rack in center of oven and preheat to 350 degrees. Butter a 13 x 9 inch cake pan and dust lightly with flour.
2. Sift flour, cocoa, baking soda and salt into a large mixer or mixing bowl and stir in the sugar.
3. Mix in the sour cream, butter, eggs and vanilla with an electric mixer on low speed. Increase to medium and mix for three minutes.
4. Transfer to the prepared pan and bake until a toothpick inserted in the center comes out clean, about 40 minutes. Cool completely, then frost with satin fudge frosting.

Fudge Frosting
1. Cut the chocolate into small pieces and set aside.
2. Combine the sugar and cream in a heavy 3 qt. pan, stirring to dissolve. Bring to a boil, then cook for 6 minutes from the time it comes to a boil. Remove from the heat and add the chocolate and butter, stirring until melted. Add the vanilla.
3. Refrigerate until well chilled, but not solid. Stir vigorously with a wooden spoon until it is soft, spreadable consistency.