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Preheat the oven to 375F.
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Grease and flour a 9- by 13-inch baking pan.
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In a small saucepan, measure 1 cup water. Add the butter, oil and cocoa and bring the mixture to a boil. Remove from the heat.
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Stir together the flour, sugar, salt and baking soda in a large bowl. Beat in the eggs, sour cream and cocoa mixture. Add the vanilla. Mix until very smooth, about 2 minutes.
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Pour the batter into the prepared pan. Bake for 25 to 30 minutes, until the center appears firm and the cake has begun to pull away from the sides of the pan. Let cool 12 to 15 in the pan before frosting.
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To make the icing, boil the butter, cocoa and milk in a medium saucepan. Remove from the heat. Stir in the sugar and beat with an electric mixer for 2 minutes. Stir in the vanilla and pecans.
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Pour warm icing over warm cake. Spread evenly. Let cool about 2 hours before cutting.