Preheat the oven to 350°F.
In a mixing bowl, combine flour, softened butter, sugar, and salt. Mix until crumbly.
Add egg yolk and cold water, mixing until a dough forms.
Press the dough into a 9-inch pie pan evenly across the bottom and up the sides. Prick the bottom with a fork to prevent bubbling.
Bake the crust for 15 minutes or until lightly golden.
While the crust is baking, prepare the filling by whisking together Greek yogurt, honey, cornstarch, vanilla extract, cinnamon, nutmeg, and eggs until smooth.
Once the crust is done, remove it from the oven and pour the filling into the crust.
Bake for an additional 25-30 minutes, or until the filling is set and slightly golden on top.
Allow the pie to cool to room temperature, then refrigerate for at least 2 hours before serving.
Serve chilled or at room temperature, topped with chopped walnuts and a drizzle of honey if desired.