In a small mixing bowl, combine the sugar and cornstarch. Whisk in the eggs until thoroughly combined.
Meanwhile, combine the evaporated milk and milk in a heavy saucepan over medium-high heat. Bring to a boil, stirring frequently. Slowly whisk 1/4 cup of the hot milk into the egg mixture. Stir for 30 seconds, then add to the milk mixture. Cook, stirring constantly until the mixture thickens, around 5 minutes. Remove from the heat and add the extract. Cool slightly and transfer to a serving bowl.