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["Make cake layers:", "Preheat oven to 350u00b0F. Butter 2 (8- by 2-inch) round cake pans and dust with flour, knocking out excess.", "Stir together milk and vinegar and set aside to ""sour"" (mixture will curdle). Melt chocolate and butter with water in a large metal bowl set over a saucepan of simmering water, whisking until smooth. Cool slightly. Sift together flour, baking soda, and salt. Beat sugar into chocolate mixture with an electric mixer. Add eggs, 1 at a time, beating well after each addition, then beat in vanilla. Add flour mixture and beat on low speed just until combined. Add soured milk and beat on high speed 2 minutes.", "Divide batter evenly between cake pans. Bake in middle of oven until tops of layers spring back when touched lightly and edges have just started to pull away from sides of pans, about 35 minutes. Cool layers in pans on racks 5 minutes. Run a thin knife around edges of pans, then invert layers onto racks to cool completely.", "Make frosting:", "Bring sugar and cream to a boil in a heavy saucepan, stirring constantly, and simmer 10 minutes. Remove from heat and add chocolate, butter, and vanilla, stirring until smooth. Transfer to a bowl and cool to room temperature, stirring occasionally. Chill frosting, stirring frequently, until thickened and spreadable.", "Assemble cake:", "Brush any loose crumbs from layers and put 1 layer upside down on a serving plate. Spread with about 1 cup frosting. Place other layer on top, right side up. Frost top and sides of cake with remaining frosting"]
