Begin by measuring all your ingredients accurately. This will ensure a smooth cooking process and a delicious final product.
In a saucepan over medium heat, combine the 400 ml milk, 80 gr sugar, and 25 gr semolina. Stir continuously until the mixture begins to thicken, about 5 minutes.
In a separate bowl, whisk together the 1 egg, 1/2 egg, 5 ml vanilla extract, 12 gr cornstarch, and the 1/2 lemon zest. Once the milk mixture has thickened, slowly pour it into the egg mixture while whisking constantly to temper the eggs.
Return the combined mixture to the saucepan and cook on low heat, stirring constantly, until it becomes a custard-like consistency, about 3-4 minutes. Remove from heat and add the 25 gr butter and 10 ml milk, stirring until the butter has melted and the filling is smooth.
Pour the filling into a prepared pie dish. Smooth the top with a spatula to ensure an even finish.
Preheat your oven to 180°C (350°F). Bake the pie for about 30-35 minutes, or until the top is golden and the filling is set.
Allow the pie to cool completely before slicing. Serve chilled or at room temperature, garnished with a sprinkle of powdered sugar or a drizzle of honey if desired.