In a three- quart heavy saucepan on low heat, add sugar, flour and salt. pour in the evaporated milk and stir constantly. The mixture will thicken slowly, about 15 mins.
Lightly, beat the egg yolks in a medium size bowl. Add a ladle full of the thickened milk mixture to the eggs and whisk. To temper the egg , add the egg mixture into the sauce pan and continue to whisk and cook until incorporated, roughly 2 to 3 minutes.( ( I add it very slowly or it will cook the eggs)
Remove the saucepan from the heat and stir in the butter and the vanilla extract,Place the pudding into a bowl and cover with with plastic wrap. Let cool in refrigerator. for 2 1/2 hours.
into a larger bowl or trifle dish add a layer of vanilla wafers,a layer of sliced bananas, and top with pudding. Add the whipped cream and then repeat the layers.Garnish with crumbled cookies on top