In a large bowl, combine flour, sugars, baking powder and salt. Add melted unsweetened chocolate, eggs, oil, juice, rum, peel and vanilla; stir to combine. Add baking chips and nuts; mix until dough is well blended.
Quarter dough; shape into 4 logs, each about 2 1/ 2" wide by 14" long.
Place 2 logs on each of 2 lightly oiled (10x15") baking pans.
Bake logs at 350 degrees just until firm to touch, about 20 min.
Cool logs slightly in pans; using a serrated knife, cut diagonally into 1/2" wide slices.
Place slices cut side down on pans; bake until crisp, about 15 min. more.
Meanwhile, in a double boiler, melt white chocolate and shortening over hot water, stirring until smoot h (or heat in a nonmetal bowl in a micro oven on 100 percent power for 15 sec. at a time, stirring after each interval, until soft and smooth, about 1 1/2 min.total). Dip 1 end of each cookie about 1" into white chocolate to coat. Lay cookies on wire racks until firm; chill to speed process.
Serve, or wrap airtight to store up to 2 days; freeze for longer storage.