Preheat oven to 350°. In a large bowl, cream butter and brown sugar until light and fluffy. Beat in flour until blended. Press into a greased 13x9-in. baking dish. Bake 12-15 minutes or until golden brown.
In a small saucepan over medium-low heat, melt caramels and butter with milk until smooth, stirring occasionally. Remove from heat; stir in confectioners' sugar and pecans. Spread over crust.
In a microwave, melt chocolate chips and shortening; stir until smooth. Drizzle over caramel layer. Cover and refrigerate 2 hours or until firm. Cut into bars.