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Grease and flour a cookie sheet and preheat oven to 400ºF.
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In a small bowl, mix the eggs, baking soda and sour cream.
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In a mixing bowl, add the flour, sugar and salt, stir to combine.
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In a medium saucepan, combine the butter, water and cocoa powder, heat and stir to combine.
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Add cocoa mixture to flour/sugar, blend with mixer. Add egg mixture and beat 1 minute. Stir in chocolate chips if desired. Put in cookie sheet and bake 14-20 minutes.
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When the cake is out of the oven, put the cream in a saucepan and heat to simmer.
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Add chocolate to the bowl of a food processor.
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Once the cream is heated, pour into food processor and let sit 4 minutes.
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Pulse a few times then process 5-10 seconds to smooth out the mixture.
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Transfer ganache to a non-plastic bowl. For a glaze style ganache, top cake now. For a lighter, fluffier "frosting", refrigerate 1-2 hours, whip in mixer, then top the cake. Top with walnuts, optional.
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Refrigerate the cake at least an hour before serving.