Pastry: In bowl, combine flour, sugar and salt. Using pastry blender or 2 knives, cut in butter until in fine crumbs. Add water; stir with fork just until moistened. Transfer to work surface and press pastry together; knead lightly 5 or 6 times just until dough forms ball. Flatten slightly into disc; wrap and refrigerate for 30 minutes. On lightly floured surface, roll out pastry into 16-inch (40 cm.) circle, leaving edges rough. Transfer to 12-inch (30 cm) pizza pan, letting pastry hang over edge.
In bowl, toss together rhubarb, sugar, flour and nutmeg. Arrange over pastry; sprinkle with pecans. Fold pastry overhang over filling. Brush pastry with milk. Bake in 425°F (220°C) oven for 10 minutes. Reduce heat to 375°F (190°C); bake for 35 to 40 minutes longer or until rhubarb is tender and pastry golden. Let cool on rack; dust with icing sugar.