Preheat the oven to 375 F (190 C). Prebake the crust for 20 minutes. When the crust is finished, remove it from the oven and reduce the temperature to 350 F (180 C).
Mix the whey, sugar, cornstarch, lemon juice, and zest in a saucepan. Whisk in the egg yolks until well combined. Then add the butter.
Slowly bring the filling to a simmer, stirring gently. Reduce heat and continue to simmer for 1 minute. After 1 minute it will have started to thicken. Pour the lemon filling into the pre-baked pie crust.
In a large bowl, beat the egg whites and cream of tartar until they form soft peaks.
Gradually beat sugar until stiff peaks form.
Stir in vanilla extract.
Dollop the meringue topping over the lemon pie.
Bake the pie on the lowest rack in your oven (to prevent the meringue from burning) for 20 minutes.
Allow to cool completely before serving.
Store in the fridge for up to 3 days.
The sugar in the lemon custard filling can be replaced with your favorite alternative sweetener. However, sugar is essential for the meringue topping.
The flavor of this pie is best with fresh, sweet whey. If you are using acid whey, then only add as much lemon juice as required to balance the acidity of the whey. Exactly how much lemon juice will depend on how acidic the whey is. The goal is to have a slightly tart flavor, without making the pie too acidic. Just taste it before you add in the egg yolks.
Keywords: traditional, treat, extra whey, winter, sweet