In a heavy bottom saucepan combine sugar, cornstarch and salt. Mix well.
Stir in water
Bring to a boil over medium heat and stirring constantly
Cook until mixture thickens, stir constantly for about 5 minutes
Remove from heat
Slowly stir a small amount of hot mixture into egg yolks to temper the eggs before adding them back to the heated sugar mixture
Bring back up to heat, stirring constantly (some recipes require the mixture be brought back up to a boil, but I find it's not necessary)
Remove from heat
Stir in lemon peel and butter
Slowly add the lemon juice until well combined and mixture is thick and shiny
Refrigerate until ready to assemble