Preheat the oven to 425°F.

Italian Meringue: Whisk the sugar and water in a small saucepan over medium heat until the sugar starts to dissolve. Stop whisking as soon as the mixture starts to simmer on the edges to prevent sugar crystals from forming. Use a candy thermometer in the mixture, and heat until the temperature reaches 240°F and the mixture has become thick and syrupy. This will take about 10-15 minutes.

While the mixture is heating up, use an electric mixer to beat the egg whites and cream of tartar in a large bowl until the egg whites are foamy. Alternatively, you can use a stand mixer with a whisk attachment. Once the syrup has reached 240°F, remove it from heat immediately, and gradually pour it into the egg whites while beating the mixture at medium speed. When all of the syrup has been poured in, bump up the mixing speed to high, and continue beating until stiff peaks have formed. Set the meringue aside.

Pie: Combine the milk, sugar, and cornstarch in a small or medium saucepan over medium heat, stirring constantly to prevent the sugar from scorching on the bottom. When the mixture thickens and starts to boil, remove it from heat.

Beat the egg yolks in a small bowl, and gradually pour in about 1/2 cup of the hot sugar mixture while whisking quickly to prevent the yolks from curdling. Place the saucepan back over medium heat, and whisk while the yolk mixture is slowly poured in. Once the custard is thick and bubbling, remove it from heat, add the salt, coconut extract, and coconut flakes, and stir.

Pour the hot custard filling into the baked pie crust and spread it out evenly. While the filling is still hot, spread the meringue on top, and use a small spoon to make small peaks and swirls in the meringue.

Bake the pie for about 7 minutes, or until the peaks and swirls start to brown. Cool the pie completely at room temperature (about 1 hour), then chill it in the refrigerator for 8 hours, or overnight. Top with toasted coconut, if desired, and serve chilled.