Lemon Curd

Steps

1. zest3 min
   fine grater, colored peel only
   lemons, taking only the yellow — the white pith underneath is bitter and contributes nothing, so stop turning the fruit the moment you see white
2. mix2 min
   fingertips, in the sugar
   zest + sugar, rubbed together until the sugar is visibly damp, clumping and smells strongly of lemon — the crystals are abrading the oil cells open, and this is where nearly all of the perfume comes from; juice alone gives you sour, not lemon
3. whisk2 min
   off heat, in a heatproof bowl
   lemon sugar + whole eggs + yolks + salt, until smooth and pale, then + lemon juice — combining everything cold works because sugar and acid raise the temperature at which the eggs coagulate, buying you a wider safe window
4. temper12 min
   bowl over barely simmering water, whisking constantly, to 170F
   the egg mixture, whisking without pause and never letting the bowl touch the water, until it thickens to the consistency of loose hollandaise, coats the back of a spoon, and a finger drawn across the spoon leaves a line that does not close — indirect heat is the whole safety margin here; direct heat is faster but scrambles the yolks at the pan floor before the center is anywhere near set
5. whisk3 min
   off the heat
   + cold butter a few cubes at a time until glossy and fully absorbed — the cold butter enriches the curd and simultaneously drops its temperature, which is what stops the cooking; the curd should look distinctly too loose at this point, because it firms considerably as it chills
6. strain2 min
   fine sieve, pressing with a spatula
   the curd, which catches the spent zest and any threads of set egg — a curd that tastes right but feels grainy is fixed here, and skipping this step is the most common reason a good curd feels homemade in the bad sense
7. rest180 min
   refrigerated, plastic wrap pressed flush to the surface
   the strained curd, until cold and set — wrap touching the surface prevents a rubbery skin. Keeps one to two weeks refrigerated, or three months frozen