Preheat your oven to 350°F (175°C) and lightly grease a 9-inch pie dish.
In a mixing bowl, combine the flour, sugar, and salt for the crust. Add the melted butter, egg, and cold water. Mix until the dough comes together.
Press the dough into the prepared pie dish, covering the bottom and sides evenly. Set aside.
In a saucepan, heat the milk over medium heat until it starts to simmer. Be careful not to let it boil.
In a separate bowl, whisk together the sugar, flour, salt, eggs, and vanilla extract until well combined and smooth.
Slowly pour the hot milk into the egg mixture, whisking constantly to prevent the eggs from scrambling.
Pour the mixture back into the saucepan and cook over low heat, stirring continuously, until it thickens to a custard-like consistency. This should take about 5-7 minutes.
Remove the saucepan from the heat and pour the filling into the prepared crust.
Sprinkle ground cinnamon evenly over the top of the tart.
Bake in the preheated oven for approximately 25-30 minutes, or until the crust is golden and the filling is set.
Allow the Melktert to cool before serving. It can be enjoyed warm or chilled.
Optionally, you can sprinkle a little extra cinnamon on top before serving.
