In small bowl beat filling ingredients together (I use a portable electric hand mixer). Set aside. Mix brownie mix according to directions on package with ingredients called for. Spread half of brownie batter into a 9 x 13" pan (grease bottom only). Drop filling over batter by tablespoonfuls over batter. Spoon remaining brownie batter over filling. Marble by pulling knife through batter in wide curves. Bake at 350 for 30 to 35 minutes (DO NOT OVERBAKE)
In small saucepan, melt chocolate and shortening together over low heat, stirring. Drizzle over cooled bars. For easier cutting, refrigerate at least 1 hour. Store, covered in refrigerator.