HEAT oven to 350°F.
BEAT cream cheese, egg and granulated sugar until light and fluffy. Stir in chocolate chunks; set aside.
PREPARE cake batter as directed on package.
SPOON into 24 paper-lined muffin cups; top each with heaping teaspoonful of cream cheese mixture. Combine sugar and nuts; sprinkle over cupcakes.
BAKE 20 min. Cool in pans 10 min. Remove to wire racks; cool completely.