In a medium sized saucepan over medium heat, add the egg yolks, sugar, and a small pinch of salt. Whisk that together continuously for about a minute or until the sugar dissolves completely.
Sprinkle in the lemon zest.
Grab a silicone spatula and continue to stir the mixture over low heat for about 10 minutes or until the custard has thickened and has a smooth, velvety texture.