Combine sugar, cornstarch, and salt in top of a double boiler. Beat egg yolks until thick and lemon colored; add to sugar mixture, mixing well. Add milk; cook over boiling water, stirring constantly, 20 minutes or until mixture is very thick and smooth.
Remove from heat; gently stir in 1 cup coconut and vanilla. Pour filling into pastry shell.
Beat egg whites (at room temperature) until foamy. Gradually add 3/4 cup sugar, 1 tablespoon at a time, beating until stiff peaks form. Spread meringue over hot filling, sealing to edge of pastry. Sprinkle with remaining coconut. Bake at 375° for 15 minutes or until meringue is golden brown. Cool to room temperature; chill.