Pistachio Cranberry Oatmeal Icebox Cookies

Name: Pistachio Cranberry Oatmeal Icebox Cookies
Ingredients: 2 sticks (1 cup) unsalted butter, softened; 1 cup packed light brown sugar; 2/3 cup granulated sugar; 1 teaspoon baking powder; 1/2 teaspoon baking soda; 1/2 teaspoon ground cinnamon; 1/4 teaspoon ground nutmeg; 1/4 teaspoon salt; 2 large eggs; 1 1/2 teaspoons vanilla; 1 1/2 cups all-purpose flour; 3 cups old-fashioned rolled oats; 1 cup roasted and salted shelled pistachios (about 5 ounces); 1 cup dried cranberries (about 4 ounces); 4 ounces bittersweet or white chocolate, melted (see Cooks' notes); A sharp serrated knife; a heavy-duty sealable plastic bag (not pleated)