In a small saucepan, whisk 1 egg until blended. Stir in 2/3 cup sugar, 1/2 cup milk and chocolate. Cook and stir over medium heat until chocolate is melted and mixture just comes to a boil. Remove from the heat; cool to room temperature.
In a large bowl, cream shortening and remaining sugar until light and fluffy. Add remaining eggs, one at a time, beating well after each. Beat in vanilla. Combine the flour, baking soda and salt; gradually add to creamed mixture alternately with remaining milk, beating well after each addition. Stir in chocolate mixture.
Pour into three greased and floured 9-in. round baking pans. Bake at 325° for 25-30 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes before removing from pans to wire racks to cool completely.
For frosting, beat cream cheese in a large bowl until smooth. Gradually add milk and peanut butter until creamy. Spread between layers and over top and sides of cooled cake. Sprinkle with peanuts. Garnish with candy bars. Store in the refrigerator.