Combine sugar, salt, and corn starch in a large saucepan. Slowly stir in milk.Cook over medium heat, stirring constantly, until mixture thickens. (Should coat the spoon) Remove from heat.
Stir in about 3 or 4 tablespoons of the hot custard mixture into the egg yolks, one tablespoon at a time. This is important because it brings the temperature of the eggs up so when you add the egg mixture to the custard it does not cook the eggs and make your custard lumpy.
Slowly stir in the egg yolk mixture into the custard mixture. Return the custard to medium heat and bring to a boil, stirring constantly. Allow mixture to boil for about a minute. Remove from heat.
Add butter and vanilla. Stir and allow mixture to cool to room temperature.
Once cooled, add lemonade, water, and evaporated milk. Stir and pour into your ice cream maker and freeze according to directions. Once freezer stops, pour into an air tight container and freeze for three or four hours (or until completely frozen). Yummmmm!