In 2-quart saucepan, mix sugar, cornstarch and salt; gradually stir in milk.
Cook over medium heat, stirring constantly, until mixture thickens and boils.
Allow to boil for 1 minute, while stirring continuously.
Gradually stir at least half of the hot mixture into egg yolks, then stir back into hot mixture in saucepan.
Boil and stir 1 minute; remove from heat. Stir in butter and vanilla.
Pour pudding into medium-sized bowl. Cover with plastic wrap (making sure it is flat against the pudding) and refrigerate about 1 hour or until chilled.
Cut bananas into 1/2" rounds; cut each round in half to create half circles.
Place wafers in plastic bag, and break into smaller pieces. (Some should be crumb sized and some should be bigger)
Place a layer of banana slices in the bottom of 4 parfait glasses.
Top each with an eighth of the pudding.
Sprinkle with an eighth of the wafer crumbs.
Repeat with layers of bananas, pudding, and wafer crumbs.
Serve with a topping of whipped cream, if desired.