Lemon Curd

Recipe found here

7 to 8 large egg yolks (about 130 grams w/o shells), depending on size
1¼ cups + 2 tablespoons (275 grams) granulated sugar
4½ fluid ounces (about 133 ml) freshly squeezed lemon juice (4 large lemons)
Pinch of kosher or sea salt
1 tablespoon (6 grams) finely grated lemon zest
½ cup (1 stick/113 grams) chilled unsalted butter, cut into pats

Add an inch or so of water to a medium saucepan or bottom pan of a double boiler set. Bring water to a simmer over medium-high heat. Meanwhile, in a medium sized metal bowl (or separate glass bowl) or top pan (insert) of a double boiler set, beat yolks and sugar vigorously with a whisk until smooth and well blended, about 1 minute. (Mixture will be very thick at first, just keep at it.) Add lemon juice and salt, whisk until smooth. If mixed in separate glass bowl, scrape and pour into top pan of double boiler set.

Once the water reaches a simmer, reduce heat to low and place bowl over saucepan or top pan (insert) into bottom of double boiler. Do not allow water to touch the bottom of the metal bowl or top pan (insert) of the double boiler as this could scorch and possibly curdle the mixture. Cook whisking constantly until thickened, about 20 to 22 minutes. The mixture will change from translucent to an opaque light yellow color and will coat the back of a wooden spoon yet still be liquid enough to pour. Do not allow the mixture to boil or it will curdle.

Remove promptly from heat and immediately whisk in lemon zest to release oils. Add butter gradually, one piece at a time, whisking well to combine. Allow each addition of the butter to melt completely before adding more. If straining (this is optional to strain lemon zest and any coagulated egg) for a smooth curd, strain at once into a medium bowl and press strainer with the back of a spoon or rubber spatula until only the coarse residue remains. Discard residue.

Allow curd to cool; cover by placing a layer of plastic food wrap directly on top of the surface of the curd. The curd will continue to thicken further upon resting and chilling. Transfer to airtight container and refrigerate.

Tips:

Before juicing lemons, heat fruit for 10 seconds in microwave oven on high power. Roll between hands or on work surface, pressing lightly on the fruit. This will release a significant greater amount of juice.

To prevent curdling, be sure to blend the sugar well with the yolks before adding the lemon juice. Use a double boiler (or a metal bowl placed over saucepan) with an inch or so of water in bottom pan or heavy nonreactive (non-aluminum) saucepan that conducts heat evenly.

Do not allow the curd mixture to boil. Remove immediately from heat once curd is thickened and, if straining (this is optional to strain the citrus zest), strain at once as the residual heat will continue to cook the curd.

 If you have an accurate candy thermometer, check the temperature of the cooked curd. It should be 170ºF. Store curd covered tightly in refrigerator. It will keep up to 2 weeks.

Warning: The reason why a nonreactive (non-aluminum) saucepan should be used is because aluminum will react with the yolks and turn them a chartreuse (green) color.