Preheat oven to 350°. In a large saucepan, combine sugar and flour. Stir in milk until smooth. Cook and stir over medium-high heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes longer. , Remove from the heat. Stir a small amount of hot milk mixture into egg yolks; return all to pan, stirring constantly. Bring to a gentle boil; cook and stir 2 minutes longer. Remove from heat; gently stir in butter and vanilla. , In an ungreased 8-in. square baking dish, layer a third of the vanilla wafers, bananas and filling. Repeat layers twice., For meringue, beat egg whites, vanilla and cream of tartar on medium speed until soft peaks form. Gradually beat in sugar, 1 tablespoon at a time, on high until stiff peaks form. Spread evenly over hot filling, sealing edges to sides of dish. Bake until meringue is golden, 12-15 minutes. Cool on a wire rack 1 hour. Refrigerate at least 3 hours before serving. Refrigerate leftovers.