Combine first 4 ingredients in a medium-size nonstick skillet. Cook over medium heat until mixture comes to a boil. Remove from heat; stir in butter. Add nuts, and gently stir to coat. Spoon coated nuts in a single layer onto a rimmed baking sheet lined with parchment paper.
Bake at 250° for 1 hour, stirring every 15 minutes. Spread nuts on wax paper or parchment paper to cool, breaking apart large clumps as nuts cool.
Melt semisweet chocolate morsels and shortening in a small saucepan over low heat, stirring until smooth. Remove from heat; cool slightly. Toss cooled nuts in semisweet chocolate until well coated. Return nuts to wax paper, and let harden. Drizzle white chocolate over nuts (do not toss). Let harden.
Tip: Speed up the chocolate hardening process by popping the jelly-roll pan into the freezer for 5 to 10 minutes.