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1
Make cake layers: Preheat oven to 350u00b0F. Butter 3 (7- or 8-inch, 2-inch-deep) round cake pans and line bottoms with rounds of wax or parchment paper. Butter paper and dust pans with flour, knocking out excess.
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2
Whisk together water, cocoa, and espresso powder until smooth, then whisk in milk and vanilla.
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3
Sift together flour, baking soda, and salt.
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4
Beat together butter and brown sugar in a large bowl with an electric mixer at high speed until fluffy, then add eggs 1 at a time, beating well after each addition. Add flour mixture and cocoa mixture in batches, beginning and ending with flour and mixing at low speed until just combined.
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5
Divide batter among pans (about 2 1/3 cups per pan), smoothing tops. Bake in middle of oven until a tester comes out clean, 30 to 35 minutes for 7-inch pans or 20 to 25 minutes for 8-inch. Cool in pans on a rack 30 minutes, then invert onto racks, remove paper, and cool completely.
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6
Make ganache while cakes bake: Bring cream to a simmer in a 3- to 4-quart saucepan and remove from heat. Whisk in chocolate until smooth. Transfer ganache to a bowl and chill, covered, stirring occasionally, until thickened but spreadable, about 4 hours. (If ganache becomes too thick, let stand at room temperature until slightly softened.)
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7
Assemble cake: Arrange 1 layer on a cake stand or plate and spread 2/3 cup ganache evenly over it. Top with another cake layer and 2/3 cup ganache, spreading evenly, then third cake layer. (Chill ganache if necessary to keep at a spreadable consistency.) Chill cake until ganache filling is firm, about 1 hour. Keep remaining ganache at a spreadable consistency, chilling when necessary.
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8
Spread ganache over top and sides of cake to seal in crumbs, then chill 30 minutes. Spread remaining ganache evenly over top and sides of cake.
