Totally got this wholesale from the wikibooks cookbook, but I managed to deviate accidentally from the recipe and am still quite pleased with the results.
1/2 cup (120ml) lemon juice
2 tablespoons freshly grated lemon zest
1/3 cup (80g) sugar
3/4 stick of unsalted butter (90g)
Pinch of salt (optional, to bring out sweetness and flavor of finished product)
I goofed in that I only used 1 tablespoon of freshly grated lemon zest. It still turned out great — doubling the lemon zest would make it quite intense, I’m sure.
Grate the lemon rinds to produce two tablespoons of zest. Grate only the yellow zest, avoid the inner white pith which is bitter. Extract the juice from the lemons to produce 1/2 cup (120ml) of juice. Cut the butter into small chunks.
Put eggs, zest, sugar, and salt into cooled sauce pan. Whisk ingredients in pan till frothy and light in color (a minute or two). Add lemon juice and whisk 30 seconds. Add butter chunks. Set pan on stove burner, turn on heat to medium-to-low, and start whisking contents so they don’t coagulate or stick to bottom of pan. Whisk constantly till butter melts and mixture thickens, then whisk another two minutes, but do not let mixture boil – it should be quite steamy (185°F, 85°C).
There’s a spot in the original recipe about here concerning the option to strain the lemon zest out of the gloop before jarring it up and letting it chill in the fridge, but I don’t believe in that. Pour mixture from bowl into jar to within 1/4 inch (0.75cm) from top, taking care not to get mixture on rim, then seal jar with lid. Refrigerate to thicken the product further.