Thaw your pie crust for 10 minutes on the counter. Whisk together the egg and tsp. of water. Using a pastry brush spread the egg wash over the pie crust. Prick the pie crust with a fork generously, even on the edges. Bake according to package directions. Mine took 12 minutes.
Zest the lemons. Cut the lemons in half and juice them, discard seeds.
Whisk the egg yolks in a small bowl, set aside. Have your butter out and ready as well.
In a medium sized sauce pan add the water, sugar, salt, lemon zest, lemon juice, flour and cornstarch, whisk together. Set the heat to medium high heat. Bring this mixture to a boil, whisking constantly.
Add the butter to the lemon mixture, stir and let melt in. Add a scoop of this hot mixture to the egg yolks bowl, stir them together. Add this egg yolk mixture to the rest of the lemon filling. Stir. Let boil for 1 more minute, whisking constantly.
Pour the lemon filling in to the prepared and baked pie crust. Refrigerate for an hour or longer.
Sour Cream Layer:
Preheat oven to 350 degrees.
In a small bowl mix together the sour cream and sugar. Spread this mixture over the lemon layer.
Bake for 7 minutes.
Remove from oven and refrigerate for at least 3 hours before making and topping with whipped cream in next step.
In a large bowl add the heavy cream and sugar. Using a hand mixer or stand mixer with whisk attachment, blend until stiff peaks form.
I used a 16 inch piping bag and a wilton 1M piping tip to decorate the pie with the whipped cream. Keep refrigerated until ready to serve.