INGREDIENTS
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2 cups all-purpose flour
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1/2 cup unsweetened cocoa powder
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1/4 cup (packed) brown sugar
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2 teaspoons baking powder
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1 teaspoon baking soda
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1 teaspoon kosher salt
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3 large eggs, separated
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2 cups buttermilk
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1/2 cup olive oil
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1 teaspoon vanilla extract
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6 oz. bittersweet chocolate (at least 70% cacao), finely chopped Nonstick vegetable oil spray
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Unsalted butter and warm pure maple syrup (for serving)