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["COOKIES: Combine the powdered sugar and pecans in a food processor fitted with a metal blade.", "Cover and process until the pecans are very finely chopped, 45-60 seconds.", "Combine the sugar mixture, butter, rum, and vanilla in a large bowl; cream with an electric mixer on medium speed until creamy, scraping sides of bowl often, 2-3 minutes.", "Reduce mixer speed to low; add the flour, baking powder, and salt, stirring until well mixed (1-2 minutes).", "Divide dough in half; shape each piece into a 10"" long roll on a lightly floured surface.", "Flatten the sides to form a triangle on a sheet of waxed paper, using the paper to help create the shape.", "Wrap each half in plastic wrap; refrigerate until firm, about 2 hours.", "Preheat oven to 375u00b0F.", "Cut each dough log into 1/4"" slices; space 1"" apart on ungreased cookie sheets.", "Sprinkle cookies with the pearl sugar; bake for 9-11 minutes, or until the edges begin to brown.", "Transfer cookies to wire racks and cool completely.", "Meanwhile, make the FROSTING: Combine all the frosting ingredients (except the half-and-half) in a small bow.", "Beat with an electric mixer on low speed, adding enough half-and-half for desired spreading consistency.", "For each sandwich cookie, spread 3/4 teaspoons frosting on the bottom of a cookie, sugar side down; top with a second cookie, sugar side up.", "Squeeze together gently; repeat until all cookies have been assembled."]