Combine pineapple and sugar in a heavy saucepan; bring to a boil. Reduce heat; simmer 20 minutes or until liquid is absorbed. Set aside.
Cream butter; gradually add powdered sugar, beating well. Add egg; beat well. Stir into pineapple. Cook over low heat 2 minutes or until saucy.
Layer 16 vanilla wafers, half of sauce, and half the nuts in an 8-inch square baking dish. Repeat layers, ending with vanilla wafers. Cover with waxed paper. Place a weight over cake. Refrigerate overnight.
Spoon cake into individual serving dishes; top with whipped cream, if desired.