Combine 1/2 Cup sugar, flour and salt in top of double boiler. Stir in 4 egg yolks and milk; blend well. Cook, uncovered, over boiling water, stirring constantly until thickened. Reduce heat to low, stirring occasionally, for 5 minutes. Remove from heat; add vanilla.
Spread a small amount on the bottom of 1 1/2 quart dish. Cover with a layer of Nilla Wafers. Top with a layer of sliced bananas. Pour 1/3 of custard over bananas. Continue to layer wafers, bananas and custard to make 3 layers of each, ending with custard.
Beat egg whites until stiff, but not dry. Gradually add remaining 1/4 Cup sugar and beat until stiff peaks form. Spoon on top of pudding, spreading to cover entire surface and sealing well to edges.
Bake 425 for 5 minutes or until delicately browned. Cool slightly, then chill.
Makes 8 1 Cup servings.