Using a 3 to 4 quart heavy-bottom saucepan over medium heat, add the granulated sugar, cornstarch and milk, and whisk. Whisk continually until the mixture reaches a low bubble and begins to thicken, about 6 to 8 minutes.
Remove the saucepan from the heat, and whisk 1 cup of the mixture into the egg yolks.
Whisk the egg yolk mixture back into the custard, and return the saucepan to the heat. Continue whisking for another 2 to 3 minutes.
Remove the saucepan from the heat. Whisk in the butter and the vanilla.
Strain the custard through a fine-mesh sieve.
Pour the custard into a heat-safe medium-size bowl or your individual serving bowls. Cover the bowl or bowls with plastic wrap, making sure to allow the plastic wrap to cover the surface of the custard to keep a “skin” from forming. Refrigerate for 2 hours before serving.
PRO TIP:You need to take extra caution with this recipe. When the custard gets heated and starts popping, you can suffer serious burns so please pay attention!PRO TIP:It is really important to keep whisking as you don’t want to burn the custard.PRO TIP:It is very important to quickly whisk the hot mixture into the yolks (temper) so you do not end up with scrambled eggs in your custard.