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1
To make filling: In a small saucepan, combine sugar, corn syrup, cocoa powder, and 1/2 cup water.
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2
Bring to a boil over medium-high heat, whisking occasionally to prevent scorching.
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3
Meanwhile, in a separate small bowl, combine cornstarch and 2 tablespoons water.
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4
Remove boiling cocoa mixture from heat; whisk in cornstarch mixture.
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5
Return saucepan to heat, and bring to a boil over medium heat, whisking constantly.
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6
Boil about 1 minute, until cornstarch is cooked and mixture is very thick.
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Remove from heat.
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8
Stir in butter and vanilla.
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9
Pour into a shallow, heat-resistant bowl; immediately cover surface with plastic wrap to prevent film from forming.
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10
Cool completely, and refrigerate until firm, or overnight.
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11
To make frosting: In a large glass bowl, combine butter and chocolates; heat in microwave (or on stovetop in a double boiler) until melted.
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Stir until thoroughly combined.
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13
In a separate bowl, combine sugar and salt.
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14
In a medium saucepan, thoroughly whisk eggs; whisk in sugar mixture, combining thoroughly.
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15
Whisk in a scant 1/2 cup water, combining thoroughly; place over medium heat and bring to 160 on a candy thermometer, whisking constantly to prevent sticking, but creating as little foam as possible.
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16
Strain mixture through fine sieve into heat-resistant container.
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17
Whisk into chocolate mixture until thoroughly combined.
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Cool completely, then refrigerate until stiff enough to spread, or overnight.
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19
To make cake: Preheat oven to 350.
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20
Grease three 9-inch round cake pans with butter; line bottoms with parchment paper, and butter the paper.
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21
In a large bowl with an electric mixer, cream together butter and brown sugar on medium speed, about 5 minutes.
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22
In a separate bowl, combine eggs and vanilla; add to brown sugar mixture in two batches, mixing on medium speed until incorporated.
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23
Scrape bowl thoroughly; beat 1 minute on high speed.
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24
Sift together cocoa powder, baking soda and salt; add to brown sugar mixture and beat on low speed until just combined.
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25
Sift flour.
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26
Add 1 cup to batter and beat on low speed until just combined.
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27
Add 3/4 cup sour cream to batter; beat on low speed until just combined.
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28
Alternate adding flour and sour cream to batter until there's none left.
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29
With mixer still running on low, slowly add hot water, beating until just combined.
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30
Scrape bowl thoroughly; beat batter on low speed about 20 seconds.
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31
Scrape bowl thoroughly once more, then divide batter evenly among the three pans, about 3 cups per pan.
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32
Bake 30 to 33 minutes, or until cake pulls away from sides of pan.
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33
Remove from oven.
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34
Cool layers in pans about 30 minutes, then remove from pans and cool completely on wire racks.
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35
Wrap in plastic and refrigerate up to one night before assembling.
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36
To assemble, level cake layers by slicing off their tops.
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37
Place bottom layer on a serving platter cut side up.
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38
Spread 1/2 cup filling on top.
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39
Place middle layer cut side down on top of bottom layer.
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40
Spread remaining filling on top.
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41
Place top layer cut side down on top of middle layer.
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42
Spread top and sides of cake with frosting.
