Preheat oven to 250 F. Oil a 10x15 inch rimmed baking sheet.
Place popcorn and nuts into a large, metal bowl, and set aside.
In a medium sauce pan, stir together the sugar, corn syrup, cocoa powder, and butter and heat over medium-high heat until mixture comes to a boil. Boil for 2 minutes and remove from heat. Stir in vanilla, then immediately pour over popcorn. Stir until the popcorn is well coated. Spread the popcorn into the prepared baking sheet. Bake in preheated oven for 30 minutes, stirring every 5 minutes. Remove from the oven, and cool to room temperature. Break any large pieces into smaller clumps. Drizzle popcorn with melted white chocolate. Allow to air dry. Store in an airtight container.