In a medium saucepan (off heat), whisk yolks, ½ cup sugar, corn starch, lemon zest, salt and ½ cup of milk until completely smooth; gradually whisk in remaining milk
Place saucepan over medium heat; bring to a gentle simmer, whisking occasionally (mixture will thicken when it reaches a simmer). Remove from heat; whisk in lemon juice.
Pour into Ginger Snap Pie Crust. Cool to room temperature, cover with plastic wrap and refrigerate for 4 hours. Top with whipped cream before serving.