4 large egg yolks
3/4 cup sugar
3 ounces lemon juice (about 2-1/2 large lemons)
2 teaspoons finely grated lemon zest
Pinch of salt
2 ounces (4 tablespoons) unsalted butter, softened
Choose a small saucepan and a metal or heat–proof glass bowl that fits securely in the top of the pan. Put 1/2 to 1 inch of water into the saucepan (just enough that the water level doesn’t quite touch the bottom of the bowl when it’s set in the pan.) Set the pan over high heat. Once it boils, turn the heat down to keep the water at a bare simmer.
Whisk together the egg yolks and sugar in the bowl until well blended.
Place the bowl on the saucepan and stir in the lemon juice, lemon zest and salt. Cook over medium–low heat, stirring constantly, for a couple of minutes. Stir in the butter, 1 ounce at a time, and continue to cook until very thick, glossy and opaque. Do not allow mixture to boil, or you’ll end up with scrambled eggs. If it starts to steam, move the pan off the heat, while continuing to stir. When the mixture cools a bit, move it back over the heat. When it’s done, it will look like a very bright, thick Hollandaise sauce.
Pour the sauce (now called curd) through a strainer. Press it with the back of a spoon to extract the sauce, but leave the coagulated proteins and zest behind.