Fill a large bowl halfway with ice and cold water. Be sure the bowl is big enough to fit the bowl your finished pastry cream will be in. Set aside.
Whisk together the egg yolks, cornstarch, and 1/2 cup of the milk in a medium bowl and set aside.
2 egg yolks, 3 tablespoons cornstarch, 1 1/2 cups whole milk
Combine the remaining 1 cup of milk, sugar and vanilla extract in a saucepan over medium heat. Bring to a simmer, stirring frequently.
1 1/2 cups whole milk, 1/4 cup granulated sugar, 1 teaspoon vanilla extract
Temper the egg mixture by drizzling a very small amount of the hot milk into the egg mixture while whisking. Very gradually add the remaining milk mixture until all of the milk is whisked into the eggs.
Pour the mixture back into the saucepan and place back on the heat whisking constantly.
As the mixture begins to thicken, whisk more vigorously. If you start to get lumps, remove the pot from the heat and whisk to break them up.
Bring the mixture to a “boil.” You should have bubbles that rise and pop in the center of the mixture as you are whisking.
Remove the pot from the heat and taste a small amount. If it has a starchy taste or feel to it, return it to the heat for a few more seconds. The final cream should be thick, smooth and taste like vanilla.
Whisk in the butter until melted and well blended.
2 tablespoons unsalted butter
Strain the pastry cream through a fine sieve into a clean bowl. This will remove any small pieces of cooked egg that may have formed. Place the bowl into the ice bath.
Allow to cool about 5 minutes, then cover with plastic wrap. When wrapping pastry cream, the plastic wrap should touch the top of the cream to prevent a skin from forming.
Chill in the refrigerator. Once chilled, the pastry cream should set.
Chilled pastry cream can now be used as desired. If your pastry cream has chilled to the point of coagulation (thick like a jello), allow it to sit at room temperature for about 30 minutes before using.