*Instructions
Whisk the egg yolks together in a medium bowl (save the egg white for meringue). Put the bowl aside.
In a medium saucepan over medium heat, combine water, sugar, flour and salt and boil, stirring constantly.
Boil for 1 minute, then slowly add the hot mixture to the egg yolk while whisking constantly. (This relieves the yolk and prevents them from cooking once they return to the heat).
Once at least half your hot mixture is added to the yolk, return the mixture (and the remaining yolk) to the stove, at low altitude, and continue to whisk hard.
Cook for another 1 minutes.
Remove from the heat again and add the butter, lemon juice and peel. Mix well and pour into the crust of the (refrigerated) pie.