In the bowl of a stand mixer using the paddle attachment beat together butter and sugar.
Slowly add in the walnuts, rum extract and salt.
Gradually add in the flour.
Cover and refrigerate the dough until well-chilled, at least 1 hour.
Heat the oven to 350 F.
Prepare a baking sheet by lining it with wax paper.
Remove the dough from the refrigerator and break into 4. Use one-fourth of the dough and return the rest of the dough to the refrigerator so it stays chilled until rolling.
Dust with flour and roll each portion of the dough to the thickness of choice (I think a thinner cookie will end up a little more crunchy so if you want a softer cookie, roll the dough about 1/8" thick)
Cut out rounds using a 2" cookie cutter.
Place the rounds on the baking sheet and bake just until the edges start to brown, about 10 minutes.
Remove the cookies and cool on a rack.
When completely cooled, spoon about 1 teaspoon strawberry jam in the center of half of one cookie and top with a second. Repeat with all of the cookies.
Keep in the fridge for 30 minutes.
Melt the chocolate chips in the microwave using a microwave-safe bowl; stir the chips every 15 seconds until melted. You can also melt the chocolate in a bain marie.
Dip the top of the sandwiches into chocolate and gently shake the excess. Place on a plate chocolate side up.
Melt the white chocolate and drizzle over sandwiches using a fork.
Store the cookies in a container and place in a cool place. They taste best the next day.