COMBINE flour, sugar and salt in a medium bowl; cut in butter with pastry blender or two knives until mixture is crumbly. Stir in water with fork just until moistened. Shape into ball; wrap in plastic wrap. Refrigerate for 30 minutes.
PREHEAT oven to 425° F.
ROLL pastry into 11-inch circle on lightly floured surface. Place in 9 or 10-inch tart pan with removable bottom. Press pastry onto bottom and up sides of pan; turn under edges and crimp. Trim if needed.
BAKE tart on baking sheet for 8 to 10 minutes or until crust is very lightly browned.
COMBINE brown sugar and flour in medium bowl; stir until well blended. Gradually stir in cream. Pour into hot crust; sprinkle with nuts.
BAKE for another 20 to 25 minutes, or until filling is bubbly. Cool completely in pan on wire rack for 1 to 2 hours.
MICROWAVE morsels and vegetable shortening in small, heavy-duty plastic bag on HIGH power for 15 seconds; knead. Microwave at additional 10-second intervals, kneading until smooth. Cut tiny corner from bag; squeeze to drizzle over tart. Garnish with nuts. Refrigerate for at least 1 hour or overnight. Let stand for 15 minutes before serving.