Begin by melting ½ cup of butter in a medium saucepan over low heat until completely liquefied.

In a mixing bowl, combine the melted butter with ½ cup of all-purpose flour and 3 tablespoons of powdered sugar. Mix until a crumbly dough forms.

Press this mixture evenly into the bottom of a greased 8x8 inch baking dish, creating a solid crust base.

Place the baking dish in a preheated oven set to 350°F (175°C) and bake the crust for 10-15 minutes until lightly golden.

Once done, remove it from the oven and allow it to cool slightly while you prepare the custard filling.

In a medium saucepan, gently heat 1 ½ cups of milk and ½ cup of granulated sugar over medium heat, stirring occasionally until warmed.

In a separate bowl, whisk together 4 egg yolks and 2 tablespoons of cornstarch until smooth.

Gradually whisk the warmed milk mixture into the egg yolk mixture to temper the eggs before returning it all to the saucepan.

Cook on low heat, stirring constantly until thickened, about 5-7 minutes.

Carefully pour the thickened custard over the pre-baked crust, smoothing out the top.

Cover the baking dish with plastic wrap and place it in the refrigerator for at least 2 hours.

After setting, use a sharp, warm knife to cut the squares into desired portions for serving.