Combine whole eggs, yolks, sugar, salt, and lemon zest in a 3-quart stainless steel saucepan, then whisk in lemon juice. Cook over low heat, stirring constantly but not vigorously, until warm to the touch, about 3 minutes. Increase heat to medium-low and continue cooking and stirring until thick and steaming-hot (custard should register 170°F on an instant-read thermometer), about 8 minutes.
3 large Eggs, 135 g Egg yolks, 270 g Granulated sugar, 1 pinch Kosher salt, 1 tbsp Freshly grated lemon zest, 310 g Lemon juice