In a medium-size mixing bowl, combine the egg yolks, cornstarch, and 1 cup of
the heavy cream. Whisk to blend well. Set aside.
Combine 2 cups of the heavy cream, the lemon juice, and sugar in a large nonreactive
saucepan over medium heat. Whisk to dissolve the sugar and bring to gentle boil.
Slowly add the egg mixture, whisking constantly as it thickens, about 5 minutes.
Be forewarned, the mixture will break. Don’t be alarmed.
Pour it into a glass bowl
and press a piece of plastic wrap down over the surface to prevent a skin from forming.
Let cool completely to room temperature.
When cooled, pour the mixture into a medium-size mixing bowl. With an electric
mixer fitted with a wire whip, beat at medium speed to recombine. If it doesn't,
warm another 1/2 cup of heavy cream and slowly add it to the mixture. Whip until
you have a thick and creamy custard.