The Preparation
In a medium saucepan, whisk together sugar and cornstarch.
Whisk in milk and lemon juice until smooth.
Cook over medium heat, stirring constantly, until the mixture comes to a boil and thickens.
Remove from heat. Temper egg yolks by slowly adding several spoonfuls of the hot mixture while whisking the yolks.
Return tempered yolks to the saucepan and stir to combine.
Add lemon zest and butter; stir until butter melts.
Allow mixture to cool to room temperature.
Fold in sour cream until fully incorporated.
Pour filling into the pre-baked pie crust.
Whip heavy cream with 2 tablespoons sugar to soft peaks.
Spread whipped cream over the pie filling.
Refrigerate uncovered for at least 2-3 hours until set.
Garnish with lemon zest or sugar before serving.
