INGREDIENTS
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1 1/2 cup unbleached all-purpose flour, plus more for pan
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1 teaspoon baking powder
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1/2 teaspoon kosher salt
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1/4 teaspoon baking soda
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8 medium-size fresh lemon verbena leaves or 1/2 teaspoon grated lemon zest
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1/2 cup (1 stick) unsalted butter, softened, plus more for pan
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2/3 cups granulated sugar
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2 large eggs, at room temperature
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3/4 cups sour cream, at room temperature
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1/2 teaspoon pure vanilla extract
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2 tablespoons firmly packed light or dark brown sugar
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12 small to medium, firm-ripe prune plums, halved lengthwise and pitted
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Lightly sweetened, softly whipped cream or crème fraîche, for serving (optional)