Combine 1/2 cup sugar, flour and salt in the top of a double boiler. Mix well. Sir in 1 egg, 3 yolks and milk. Mix well. Place over boiling water. Cook, stirring constantly, until smooth and thickened.
Remove the mixture from the heat and stir in the vanilla. Spread 1/4 cup of the pudding in a 1 3/4 quart casserole. Arrange 12 wafers over the pudding. Top with 1/3 of the banana slices and 1/3 of the remaining pudding. Repeat the layers twice.
Beat 3 egg whites (at room temperature), at the high speed of an electric mixer, for 1 minute. Gradually add 1/4 cup sugar, 1 tablespoon at a time. Beat until stiff peaks form and the sugar dissolves (2-4 minutes). Spread the meringue over the pudding, sealing to the edge of the casserole.
Bake at 350°F for 12-15 minutes or until golden brown.