Preheat the oven at 350F. In a non-stick medium pot, add the milk, butter, sugar, and vanilla; bring to a boil, and reduce heat to low. In a large bowl, add the eggs and the cornstarch and mix well. Slowly add 1 cup of the milk mixture, mixing constantly to temper the eggs. Keep adding more milk until the mixture is soft and has no lumps. ​ Add the mixture to the pot SLOWLY and mix constantly using a wooden spoon. Keep cooking and mixing for a few more minutes until the mixture gets thick, you will know when it is ready when passing a spoon at the bottom of the pot creates a line that separates the mixture.

Remove from heat and pour into the pyrex (no need to grease it ( I use an 11 by 8-inch pyrex). Cover with foil and cook for approximately 50 min. Remove the foil after 30 min of cooking to allow the top to get a light brown color. Let it cool completely before serving.