Preheat your oven to 350°F (175°C).

In a mixing bowl, combine the flour, sugar, and salt. Add the softened butter and mix until the mixture resembles coarse crumbs.

Press the mixture evenly into the bottom of an 8-inch square baking dish. Bake for about 15-20 minutes until lightly golden.

While the crust is baking, heat the milk in a saucepan over medium heat until warm but not boiling.

In a separate bowl, whisk together the egg yolks, sugar, cornstarch, and a pinch of salt. Gradually whisk in a little of the warm milk to temper the egg mixture.

Pour the tempered mixture back into the saucepan with the remaining milk. Cook over medium heat, stirring constantly, until the mixture thickens and bubbles. Remove from heat and stir in the vanilla extract.

Pour the custard filling over the baked crust, spreading it evenly. Allow it to cool to room temperature before refrigerating for at least 2 hours.

Once chilled, cut into squares and dust with powdered sugar, if desired.