Chocolate Cake with Chocolate-Pecan Frosting

Description
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Ingredients

 * 2 cups all-purpose flour
 * 2 cups granulated sugar
 * 1 teaspoon baking soda
 * Pinch of salt
 * 8 tablespoons (1 stick) unsalted butter, cut up
 * 8 tablespoons (1 stick) margarine, cut up
 * 1 cup water
 * 1/3 cup unsweetened cocoa powder (not Dutch process)
 * 3/4 cup sour cream
 * 2 large eggs
 * 1 teaspoon vanilla extract
 * Frosting
 * 8 tablespoons (1 stick) unsalted butter, cut up
 * 1/3 cup plus 1 tablespoon milk
 * 1/4 cup unsweetened cocoa powder (not Dutch process)
 * 1 pound (about 4 1/3 cups) confectioners' Sugar, sifted
 * 1 teaspoon vanilla extract
 * 1 cup (4 ounces) coarsely chopped pecans, toasted
 * 1 cup (4 ounces) coarsely chopped pecans, toasted

Directions
To make the cake:

Position a rack in the center of the oven and preheat to 350 °F. Lightly butter and flour a 13 x 9-inch baking pan, tapping out the excess flour. Whisk the flour, granulated sugar, baking soda and salt in a large bowl to combine. In a medium saucepan, bring the butter, margarine, water and cocoa to a boil over high heat, stirring to dissolve the butter and margarine. Pour into the flour mixture and whisk well. Add the sour cream, then the eggs and vanilla, and beat well. Spread evenly in the pan. Bake until the cake springs back when pressed in the center, about 35 minutes. Remove from the oven and place on a wire rack.

To make the frosting:

Bring the butter, milk and cocoa to a boil in a large saucepan over medium heat, stirring to dissolve the butter. Gradually stir in the confectioners' Sugar, then the vanilla. Stir in the chopped pecans. Pour over the warm cake. Cool the cake in the pan on the rack. Cut into pieces and serve directly from the pan.