INGREDIENTS
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1 stick unsalted butter, melted and cooled, plus more for pan
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2 cups unbleached all-purpose flour, plus more for pan
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1 3/4 cups granulated sugar
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1/4 cup unsweetened cocoa powder
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2 1/4 teaspoons baking powder
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1 1/2 teaspoons kosher salt
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1/2 teaspoon baking soda
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4 large eggs, beaten
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2 teaspoons pure vanilla extract
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3 cups coarsely grated zucchini (from 1 pound)
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5 ounces semisweet chocolate, chopped (1 cup)
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1 1/4 cups confectioners' sugar
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1 to 2 tablespoons whole milk
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1 teaspoon poppy seeds