Line a large baking sheet with foil; set aside. In a heavy medium saucepan, heat candy coating and white baking chocolate over low heat, stirring frequently until melted and smooth. Remove from heat.
Stir in 1/2 cup of the crushed candy. Pour mixture onto the prepared baking sheet.; spread to about 3/8-inch thick. Sprinkle with remaining crushed candy and macadamia nuts, if you like; press slightly.
Chill candy about 30 minutes, or until firm. (Or let candy stand at room temperature for several hours until firm.) Use foil to lift firm candy from the baking sheet; carefully peel off foil and break candy into pieces.
To store, layer the pieces of candy between waxed paper in airtight container; cover. Store in refrigerator up to 2 weeks, or freeze up to 3 months. Serve at room temperature. Makes about 1-3/4 pounds (about thirty-six, 2-inch pieces.).