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