Place popcorn in large bowl sprayed with nonstick cooking spray; set aside.

Line baking sheet or work surface with waxed paper or foil.

In large saucepan, stir sugar, cocoa, instant coffee and milk. Cook until mixture registers 250 F on candy thermometer, stirring occasionally.

Pour hot mixture over popcorn; stir to coat popcorn completely.

Spread popcorn onto prepared surface and allow to cool. Sprinkle with powdered sugar.

Break into pieces to serve. Store in airtight container.