In a large saucepan, whisk together 1/2 cup sugar, flour and salt. Whisk in egg yolks and milk until no lumps remain. Cook over medium-low heat, stirring constantly until thickened, about 10 minutes. Remove from heat and stir in vanilla.
Slice bananas 1/4-inch thick and toss with lemon juice (if using).
In a 2-quart baking dish, add a layer of vanilla wafer. Top with half the bananas and half of the pudding. Repeat layers.
For the meringue:
With an electric mixer, beat egg whites and cream of tartar on medium speed until soft peaks form (about 30 seconds). Gradually add 1/4 cup of sugar, 1 tablespoon at a time and increase speed to high until stiff peaks form.
Spread meringue over pudding, making sure meringue touches edges of dish. Bake for 5-7 minutes, or place under broiler until meringue is lightly toasted. Cool and refrigerate before serving.