Separate eggs; place yolks into a medium heatproof bowl and whites in a large mixer bowl. Set aside. In a medium saucepan, whisk together ½ cup sugar, flour, and salt. Slowly whisk in milk. Cook and whisk over medium-high heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes longer. Remove from heat.
Stir a small amount of the hot milk mixture into egg yolks to temper, then mix in the rest. Return all to pan; bring to a gentle boil for 2 minutes, stirring constantly. Remove from heat again and stir in butter and 1 teaspoon vanilla. Set aside to cool. In an ungreased 9-inch square baking dish, layer half the vanilla wafers, bananas (cutting in ¼- to ½-inch slices as you go), and custard. Repeat layers.
Preheat oven to 350 F. For meringue, beat egg whites, cream of tartar, and vanilla on medium speed until soft peaks form, about 5 minutes. Gradually beat in sugar, about a teaspoon at a time, on high until stiff peaks form and the surface is smooth and glossy, 5 to 7 minutes. With a spatula or spoon, dollop meringue over custard, creating peaks and sealing to the edges. Bake 8 to 10 minutes, until meringue tips are golden brown. Cool 30 minutes. Serve at room temperature or chill in refrigerator first.
Per serving: 501 calories, 15 grams fat (6 grams saturated fat), 117 milligrams cholesterol, 234 milligrams sodium, 83 grams total carbohydrates, 3 grams fiber, 10 grams protein.
