In a medium saucepan, gently heat 2 cups of milk over medium heat. Warm the milk until you see bubbles starting to form around the edges, but don’t let it come to a full boil. Turn off the heat and let it cool slightly.
In a separate bowl, whisk together 4 egg yolks, 1/3 cup of sugar, and a pinch of salt until the mixture is light and fluffy. If you prefer a thicker custard, whisk in 1 tablespoon of cornstarch at this point. The cornstarch will help thicken the custard without altering the flavor.
To avoid scrambling the eggs, you’ll need to temper them. Slowly pour a small amount of the heated milk into the egg mixture while whisking continuously. Gradually add the remaining milk, ensuring you keep whisking to prevent the eggs from cooking too quickly.
Pour the tempered egg mixture back into the saucepan. Cook the custard over low heat, stirring constantly with a whisk or wooden spoon. The custard will gradually thicken as it heats. You’ll know it’s ready when it coats the back of a spoon and holds its shape. This should take about 10 minutes.
Once thickened, remove the saucepan from the heat. Stir in 1 teaspoon of vanilla extract for flavor.
To ensure a smooth texture, strain the custard through a fine mesh strainer into a clean bowl or directly into your serving dishes.
Let the custard cool to room temperature before serving, or refrigerate it for a chilled dessert. You can serve it plain or with toppings like fresh fruit, caramel, or a dusting of cinnamon.