In a medium sized bowl, whisk together the cornstarch and sugar, then add the eggs and whisk until smooth. Set aside.
¼ cup cornstarch, ½ cup granulated sugar, 2 large eggs
Prepare a large bowl with a fine mesh strainer – you will need this immediately after your pastry cream comes off the heat.
Pour the milk and salt into a medium saucepan over medium-high heat and bring it to just under a boil, stirring occasionally so you don’t burn the milk solids on the bottom of the pan.
2 cups whole milk, ¼ teaspoon kosher salt
Once the milk is simmering well, add ⅓ of the milk to the egg mixture and whisk constantly. Pour the egg mixture into the saucepan with the rest of the milk and return to medium high heat.
Whisking vigorously and constantly, the mixture will begin to thicken and you will see the small milk bubbles start to disappear. Once this has happened, the mixture will quickly thicken and boil. Allow it to boil for about 30 seconds, then remove it from the heat and pass it through the sieve into the bowl. Use the whisk/rubber spatula/wooden spoon to mix the custard around to get it through the sieve.
Allow the pastry cream to cool to 140℉, then whisk in one tablespoon of butter at a time. Don’t add a new piece until the other has been fully incorporated. Once all butter has been added, add the vanilla and mix to combine. Cover the bowl with plastic wrap and press the wrap directly on the pastry cream so it doesn’t form a skin. Put the pastry cream in the fridge to chill for at least 3 hours.
¼ cup unsalted butter, 1 teaspoon vanilla paste or extract