Separate egg yolks from whites and save whites for another use. Beat egg yolks and ¼ cup chopped banana in a medium bowl. Then whisk in sugar, flour, and salt until well combined and falls off the spoon in thick ribbons.
In a saucepan heat milk just until bubbles start to form around the edge.
Whisk a small ladle of the hot milk into the beaten egg yolk mixture. Add one more ladle whisking continuously to bring to temp without scrambling the eggs.
Add entire egg yolk mixture to remainder of hot mixture in saucepan. Stirring constantly cook until beginning to bubble, about 8 minutes more. Once bubbly cook about 2 minutes longer to thicken.
Remove pudding from the stove, whisk in remaining ¼ cup chopped banana, butter and vanilla. Stir until smooth.
Pour half the pudding into individual banana pudding cups. Add 1-2 slices of banana on each serving then top with remaining banana pudding.
Using a spoon or offset spatula gently push pudding down to cover banana slices and prevent them from browning.
Place plastic wrap over surface and refrigerate until cooled, 1 hour or more.
Meanwhile, whip cream. Using a cold mixer and cold cream whip on medium speed until frothy then increase to high and add powdered sugar. Continue whipping until stiff peaks form. Before serving, top with whipped cream and garnish with a vanilla wafer and/or banana slices.