FOR THE CRUST
Cream the butter and add the sugar. Beat in the egg. Stir in the flour and salt. Knead until a soft dough has formed. Chill for 10 minutes.
Roll the dough out onto a lightly floured surface and layer it into a greased pie dish. Cover with a sheet of baking paper and fill the void with pie weights. Prebake at 350 degrees for 15 minutes. Remove baking paper and pie weights. Allow crust to cool completely on a wire rack.
TIP: you can use plain rice instead of pie weights to prevent the crust from forming air pockets.
FOR THE FILLING
In a heat proof bowl, whisk together the eggs, sugar, cornstarch, flour and vanilla. Set aside.
In a medium size saucepan, heat the milk and butter at medium setting. Do not bring to a boil.
Add about a quarter of the milk to the egg mixture, whisking to incorporate it evenly. Pour the mixture back into the saucepan with the remainder of the milk. Return to heat and stir constantly until it thickens. Do not boil!
Pour the filling into the pie crust and let cool completely. Refrigerate until serving. Sprinkle with cinnamon before serving.