Slice mangoes in half along the widest part, and remove the seed. Scoop the flesh out of the skin with a large spoon, and transfer to a food processor. Puree the mango, and set aside.
In a saucepan, stir together the cornstarch, sugar, flour and salt. Gradually stir in milk so that no lumps form. Cook over medium-low heat, stirring constantly until the mixture begins to bubble. Remove from heat, and stir in the mango puree until well blended. Stir in the amaretto.
Pour the mixture into a 9x13 inch glass dish, and cover the surface with plastic wrap. Freeze until firm.