In a 3-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 minutes.
Lightly beat the egg yolks in a medium size bowl. Add a ladleful of the thickened milk mixture to the eggs and whisk, to temper the eggs. Add the egg mixture into the saucepan and continue to whisk and cook until incorporated, roughly 2 to 3 minutes.
Remove the saucepan from the heat and stir in the butter and the vanilla extract. Place the pudding into a bowl and cover with plastic wrap. Let cool in refrigerator for 2 1/2 hours.
Into a large 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.