Make your pie crust and let it cool. Scald 2 cups of milk with the sugar and salt in a heavy medium size saucepan over low heat. Stir occasionally to dissolve sugar. Dissolve the cornstarch in the remaing 1/4 cup milk in a small bowl. Whisk in the egg yolks.
Whisk the egg mixture into the scalded milk. Cook, whisking constantly, over low heat until it thickens and bubbles, about 3 minutes, then cook for 1 minute more. The custard should form loose mounds when dropped from a spoon back into the pan.
Remove the custard from the heat and stir in the butter and vanilla. Tranfer the custard to a small bowl and cool for 15 minutes, gently stirring several times to allow the steam to escape. Place a piece of plastic wrap directly on the surface of the custard and take your kitchen sheers and cut 3 slits in the plastic. Cool for 30 minutes in the refrigerator.
While the custard is cooling, cut the bananas into 1/4-inch-thick slices and toss them with the lemon juice to prevent them from turning brown.
Spread half the cooled cutard in the pie shell and cover it with a layer of bananas, Spread the remaining custard carefully over bananas and arrange the remaining bananas on top. Spread top with whip cream or merigue. (I browned my meringue in the oven) Chill the pie for atleast 2 hours before serving.