Heat milk with half of the sugar in a pot.
In a bowl mix egg with the other half of the sugar, semolina, cornstarch and vanilla extract.
Temper egg mixture with the hot milk.
Transfer back in the pot and boil.
Off heat add butter and lemon zest. Let cream.
Once cool down mix in a blender to fine the texture.
Cover the bottom of a steel pastry ring 14 cm ( 5½ inches) diameter with aluminum foil. Brush butter on the inside and on the bottom. Cover with baking paper.
Pour in the milk pie mixture.
Top up with the egg wash and cover all the surface.
Bake at 170 °C/ 338 ℉ for 35 - 45 minutes. Let cool and sprinkle with cinnamon powder.