"These cookies from Lisa Yockelson are made with rich chocolate frosting and crisp sugar cookies...."
INGREDIENTS
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4 cups bleached all-purpose flour
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1 teaspoon baking soda
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1 teaspoon cream of tartar
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1/2 teaspoon salt
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1/2 pound unsalted butter, softened
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1 cup plain vegetable oil (such as canola)
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1 cup superfine sugar (or just blitz granulated sugar in a blender until finely ground but not powdery)
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1 cup confectioners' sugar
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4 large egg yolks
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2 1/2 teaspoons vanilla extract
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4 cups confectioners' sugar, or more as needed
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1/8 teaspoon salt
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6 ounces unsweetened chocolate, melted and cooled to tepid
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2 1/2 teaspoons vanilla extract
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1/2 cup plus 1 tablespoon milk, heated to tepid
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8 tablespoons unsalted butter, softened