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1
Preheat the oven to 325u00b0F.
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2
Grease and flour the insides of two 14-14.5 ounce cans.
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3
Place the cans on a baking sheet, and set aside.
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4
Whisk the buttermilk, egg yolk, and vanilla together in a small bowl.
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5
Gradually pour the melted butter into the buttermilk mixture, whisking constantly.
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6
Sift the flour, cocoa powder, baking soda, and salt into a medium-size mixing bowl; add sugar, and then whisk to blend well.
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7
Add the buttermilk mixture and whisk just until the dry ingredients are moistened.
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8
Divide the batter between the prepared cans.
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9
Bake the cakes until a toothpick inserted into the center comes out clean, 25 to 30 minutes.
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10
Place the cans to a wire rack to cool for 15 minutes.
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11
Run a knife around the edge of each can and invert them to release the cakes.
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12
Turn the cakes upright and let them cool completely on the rack.
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13
Meanwhile, make the frosting: Place chocolate in the top of a double boiler set over simmering water, and heat, stirring occasionally, until melted. (May also do this in the microwave.).
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14
Let the chocolate mixture cool for 5 minutes. Then add the sour cream, vanilla, and salt, and whisk to blend well.
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15
Let the frosting cool to room temperature, stirring it occasionally.
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16
When frosting and cakes have cooled, cut each cake in half horizontally.
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17
Spread a layer of frosting about 1/2 inch thick on the cut side of one cake half, then stack the other half on top of it.
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18
Frost the top and sides of the cake.
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19
Repeat with the remaining cake and frosting.
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20
Store the cakes in the refrigerator in an airtight container, bringing them back to room temperature before serving.
