INGREDIENTS
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2 cups flour
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1/2 cup Dutch-process cocoa powder, such as Droste
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1 1/2 teaspoons baking soda
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3/4 teaspoon fine sea salt
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1/2 cup unsalted butter, at room temperature
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1 cup packed dark brown sugar
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1 large egg
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1 teaspoon vanilla extract
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1 vanilla bean, split lengthwise and seeds scraped out
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1 cup buttermilk
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1 1/2 cups powdered sugar
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1 1/2 tablespoons matcha*
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3 ounces cream cheese
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mascarpone
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6 tablespoons unsalted butter, at room temperature