Step 1 In the bowl of a stand mixer using the paddle attachment, or in a large bowl using a hand mixer, beat together the butter and sugar. Slowly beat in the walnuts, rum and salt. Slowly beat in the flour. Cover and refrigerate the dough until well-chilled, at least 1 hour.
Step 2 Heat the oven to 350 degrees. Remove the dough from the refrigerator and break off one-fourth of the dough; return the rest of the dough to the refrigerator so it stays chilled until rolling. Roll each portion of the dough to a thickness of 3 millimeters (a scant one-eighth of an inch); if the dough is a bit sticky, roll it under a layer of plastic wrap or dust the dough lightly with flour. Cut out rounds using a 2-inch cookie cutter. Place the rounds on a baking sheet and bake just until the edges start to turn brown, 10 to 12 minutes. Remove the cookies and cool on a rack.
Step 3To assemble the cookie sandwiches, spoon about 1 teaspoon raspberry jam in the center of half of one cookie and top with a second. Repeat with all of the cookies.
Step 4Melt the chocolate chips in the microwave using a glass microwave-safe container; stir the chips every 10 seconds until melted. The chocolate can also be melted in a metal bowl set over simmering water, stirring until all of the chips are melted. Place the melted chocolate into a piping bag or into a heavy, sealable plastic bag with one of the corners cut off, and glaze the cookies. Garnish with dark and white chocolate curls for an extra special treat.
Step 5Store the cookies in a tin container and place in a cool place at least overnight, to give the flavors time to develop.