In a medium bowl, combine the flour, brown sugar, 1/2 cup of butter and the egg yolks. Mix together by hand until everything is well blended, and the mixture is crumbly. Press evenly into a 9x13 inch pan.
Bake for 12 to 15 minutes in the preheated oven, until light gold.
As soon as the crust comes out of the oven, sprinkle the 2/3 cup of chocolate chips onto it. Return to the oven for 1 to 2 minutes. Take out of the oven and spread the melted chocolate chips over the crust. Set aside.
In a medium bowl, mix together the confectioners' sugar, peanut butter,1/4 cup of margarine, and vanilla. Then stir in the milk. Crumble the peanut butter mixture over the chocolate layer. Press down lightly. In a medium saucepan, combine the 1/3 cup chocolate chips and the shortening. Cook over low heat, stirring occasionally until melted. Drizzle over the peanut butter layer and refrigerate until set, about 3 to 4 hours. Cut into 2x 1 1/2 inch bars