In a large mixing bowl combine the brown sugar, tapioca, cinnamon, nutmeg, and dash salt.
Stir in plums.
Let stand 15 minutes.
Turn mixture into an 8x1 1/2-inch round baking dish.
Dot with butter.
Prepare and roll out pastry to a 9-inch circle.
Cut slits for escape of steam.
Place over plum filling.
Trim pastry; flute to side of dish but not over edge.
If desired, garnish top of pie with pastry cutouts made from pastry trimmings.
To prevent over browning, cover edge of pie with foil.
Bake in 375" oven for 20 minutes.
Remove foil; bake for 20 to 25 minutes longer or till crust is golden.