Prepare and roll out pastry.
Line a 9-inch pie plate.
Trim pastry to 1/2 inch beyond edge of pie plate.
Flute edge and prick bottom and sides of pastry with tines of a fork.
Bake in 450° oven for 10 to 12 minutes or till golden.
Cool on rack.
Drain pineapple, reserving syrup.
Add enough water to syrup to measure 1 cup liquid.
In saucepan heat the 1 cup liquid to boiling; remove from heat.
Add gelatin; stir till gelatin is dissolved.
Add pineapple or lemon sherbet by spoonfuls, stirring till melted.
Chill till mixture mounds when spooned.
Fold in crushed pineapple.
Turn mixture into baked pastry shell.
Chill several hours or overnight till set.
Garnish with whipped cream.
Cover; chill to store.