Preheat oven to 350. For crust, in medium bowl, stir together flour and brown sugar. Using a pastry blender, cut in butter til mixture resembles coarse crumbs. Press onto bottom of ungreased 13 x 9 inch baking pan. Bake for 15 minutes. Sprinkle pecans and coconut over hot crust.
Meanwhile, for filling, in small bowl, mix sweetened condensed milk and vanilla. Carefully pour over pecans and coconut. Spread evenly.
Bake for 25 to 30 minutes or til filling is set. Cool in pan on wire rack for 10 minutes.
Meanwhile, in small pan, mix caramels and milk. Cook and stir over medium low heat just til caramels are melted. Drizzle caramel mixture over filling. Sprinkle with chocolate pieces. Cool completely. Cut into bars. Makes 24 bars.
To store, layer bars between sheets of waxed paper in an airtight container, and cover. Store at room temperature for up to 3 days or freeze for up to 3 months.