Place the sugar, flour, evaporated milk, egg yolk, vanilla, and cornstarch in a medium-sized bowl. Whisk the mixture until it is thoroughly combined.
Pour the mixture into the pie crust (not prebaked). Pour about two tablespoons of sugar on a plate. Using a pastry brush, dip the brush into the filling and then into the sugar and coat the portion of the pie crush above the level of the filling. Continue dipping the brush and coating until the entire exposed area is covered.
Place the pie into the oven and bake for 45 minutes. If filling is not yet set, continue baking for 5-10 minutes. Remove from oven and cool.