Line a 13 by 9-inch cookie sheet with waxed paper, allowing 2 inches of paper to hang over sides. Melt all but 1/4 cup of semisweet chocolate morsels in microwave on medium power for 2 minutes, stirring every 30 seconds, or until smooth. Pour chocolate onto prepared sheet and spread to cover entire surface and form 1 even layer. Melt all but 1/4 cup of white chips in microwave on medium power for 2 minutes, stirring every 30 seconds, or until smooth. Drizzle melted white chocolate over semisweet chocolate layer. Using a toothpick or skewer, swirl the melted chocolates together, creating a marbled effect.
Place nuts in a plastic bag and crush, using a rolling pin. Sprinkle chocolate with nuts and remaining semisweet and white morsels. Gently press toppings into melted chocolates. Refrigerate for 30 minutes, or until chocolate is firm. Remove waxed paper from chocolate. Cut or break chocolate into bite-size pieces.