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Preheat oven to 350 with rack in the center.
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Spray two 8" round cake pans with nonstick spray.
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Whisk dry cake ingredients together in a large mixing bowl.
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Combine water, oil, vinegar, instant coffee granules, and vanilla in a large measuring cup.
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Add to the dry ingredients and whisk until combined- a few lumps are ok.
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Divide batter between the two pans (about 3 cups each), then bake until toothpick inserted in center comes out clean (35- 40 min).
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Cool cakes for 15 minutes on a rack, then invert them onto the rack.
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Leave upside down until completely cooled before frosting them.
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To make icing, melt butter in large saucepan over medium heat.
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Stir in sugar, cocoa, and salt- the mixture will be thick/grainy.
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Combine cream, sour cream and coffee granules in a large measuring cup, mixing until smooth.
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Gradually add cream mixture to chocolate until blended and smooth.
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Cook until sugar has dissolved, and mixture is smooth and hot to the touch.
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DO NOT BOIL.
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Take mixture off the heat, and add vanilla.
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Cool at room temperature until spreadable (up to three hours).
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If it isn't getting thick enough to be spreadable, put in the refrigerator until thick enough to spread.
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If it gets too thick to spread easily, warm gently in the microwave until it's just right (20 seconds or so, repeat if necessary).
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Stir well, and ice cake, frosting first layer, then placing second layer on top, and icing the top and then the sides.