Combine first 3 ingredients in a heavy saucepan. Whisk in milk and egg yolks until blended. Bring to a boil over medium heat. Boil, whisking constantly, 16 minutes or until thickened. Remove from heat; stir in 1/2 cup coconut and 1 teaspoon vanilla.
Arrange banana slices in bottom of baked Pastry; pour custard over banana.
Beat egg whites, cream of tartar, and 1/8 teaspoon salt at high speed with an electric mixer until foamy. Add 1/3 cup sugar, 1 tablespoon at a time, beating until stiff peaks form and sugar dissolves (2 to 4 minutes). Stir in remaining 1/4 teaspoon vanilla. Spread meringue over hot filling, sealing to edge of Pastry.
Bake at 325° for 20 minutes or until golden brown. Sprinkle with remaining 1/2 cup coconut.